Backend

200 OK is the server's way of saying 'yep, everything worked great, here's what you asked for.' It's the best number to see in your network tab.

201 Created is like 200 but specifically for when something NEW was made.

301 Moved Permanently means 'this URL has moved forever — update your bookmarks.' It's the server politely telling you to go somewhere else permanently.

400 Bad Request means 'you sent me garbage and I don't know what to do with it.

401 Unauthorized means 'who are you? Log in first.' You haven't proven your identity.

403 Forbidden means 'I know who you are, but you're not allowed in here.' You're authenticated but not authorized.

404 Not Found is the internet's most famous error — 'that thing doesn't exist.

500 Internal Server Error means the server tried to handle your request and something exploded on its end. It's not your fault — the server messed up.

A/B testing backend is the server-side logic that splits users into groups and tracks which version performs better.

An API is like a menu at a restaurant. The kitchen (server) can do a bunch of things, but you can only order what's on the menu.

API documentation is the instruction manual for your API. It tells other developers what endpoints exist, what data to send, and what they'll get back.

An API gateway is the front door for all your microservices.

API Rate Limiting is the velvet rope of the internet — it controls how many requests you can make in a given time period. It's like a bouncer saying 'you'v

API versioning is how you update your API without breaking everyone's apps.

ASGI is WSGI's younger, cooler sibling that can handle async stuff.

Active Record is an ORM pattern where each database row becomes an object that knows how to save itself.

Actix is a Rust web framework that's basically a speed demon.

AdonisJS is what happens when a Node.js developer gets jealous of Laravel and Rails.

An aggregate root is the boss entity that controls a group of related objects. Want to add an item to an order?

Kafka is like the world's most reliable postal service, except instead of delivering letters, it delivers millions of messages per second and never loses o

Pulsar is like Kafka went to college and came back with a multi-tenancy degree and a tiered storage minor. It separates the serving layer from the storage

At-least-once delivery guarantees every message gets delivered... but maybe more than once. If the acknowledgment gets lost, the message gets sent again.

At-most-once delivery is fire-and-forget messaging. The message gets sent once and if it's lost, oh well. No retries, no duplicates.

Auth is just the shorthand that developers use for both authentication and authorization combined.

BFF means building a dedicated backend for each frontend. Your mobile app needs different data than your web app, so why force them to share one API?

A background job is work your app does behind the scenes that the user doesn't wait for.

Batch loading is fetching many things in one call instead of one at a time. Instead of asking 'give me user 1... give me user 2... give me user 3...

A digital ledger that nobody owns but everyone can verify.

The body is where the actual data lives in a request or response. It's the message inside the envelope.

Bruno said 'what if your API collection was just files in your git repo?' Collections are stored as .

The bulkhead pattern isolates different parts of your system so one failure doesn't sink everything. Named after ship bulkheads that contain flooding.

Bun is a JavaScript runtime (like Node.js) that does everything faster — starting up, installing packages, running tests, bundling code.

Bun is the new kid that wants to replace Node.js, npm, and webpack all at once.

CDC is the acronym for Change Data Capture — streaming database changes as events in real-time. See the full 'Change Data Capture' entry for details.

A CQRS handler is the function that actually does the work when a command or query comes in. Command handlers change state (create, update, delete).

CSV is the simplest way to share table data — just rows of values separated by commas. It's what you export from Excel.

Caching is saving the result of a slow operation so you can reuse it quickly next time.

A canary backend routes a small percentage of traffic to a new version of your service while most users stay on the old one.

Celery is Python's way of saying 'I'll do that later.

Change Data Capture (CDC) watches your database for changes and streams them as events.

Chaos testing is intentionally breaking things in production to see if your system can handle it. Kill a server. Slow the network.

A child process is when your Node.js app spawns a completely separate process to do work.

A circuit breaker stops calling a failing service after too many errors, just like an electrical circuit breaker cuts power to prevent a fire.

The client is YOU — or more specifically, your browser or app. It's the thing that makes requests to the server. The client asks, the server answers.

The command pattern turns requests into objects. Instead of calling a function directly, you create a 'command' object that describes what you want done —

A conditional request asks the server 'has this changed since last time I checked?' If not, the server saves bandwidth by just saying 'nope.

A connection pool pre-opens a bunch of database connections and reuses them instead of opening a new one for every request.

Consul is HashiCorp's tool for service discovery, health checking, and configuration.

Content negotiation is when the client and server agree on what format to use for the response.

A controller is the manager who actually handles your request after it passes through security.

A core dump is a snapshot of a program's memory at the moment it crashed — the crime scene photo of a software death.

A correlation ID is like a tracking number for a request as it bounces between microservices.

A cron job is a task that runs on a schedule automatically. 'Every day at midnight, clean up old sessions.' 'Every hour, send digest emails.

Cursor pagination uses a 'you are here' bookmark instead of page numbers. After getting results, you get a cursor (pointer) to the last item.

Cursor-based pagination is like using a bookmark instead of a page number. Instead of saying 'give me page 47,' you say 'give me the next 20 items after th

DLL hell is the Windows version of dependency hell. Your app needs version 1.0 of a DLL. Another app installed version 2.0.

DataLoader batches and caches database calls in GraphQL. Without it, fetching 100 users with their posts makes 101 database queries (the N+1 problem).

An assembly line for data. Raw data goes in one end, gets cleaned, transformed, enriched, and validated at each station, and comes out the other end ready...

Banking without banks. Lending, borrowing, trading, and earning interest — all through smart contracts instead of institutions.

A backend decorator wraps a function or class to add extra behavior without modifying the original.

Deno is a JavaScript runtime created by the same person who made Node.js — as a 'do-over' to fix Node's mistakes.

Deserialization is the opposite of serialization — it's unpacking the flat box (JSON) back into a real usable object in your code.

Distributed tracing is request tracing's big brother — it works across multiple services, servers, and even data centers.

Django is the 'batteries included' Python web framework. It comes with an ORM, admin panel, auth system, form handling, and more — all built in.

A domain event is something meaningful that happened in your business. Not 'row updated in users table' but 'UserRegistered' or 'OrderShipped.

Drizzle is the ORM for developers who think Prisma is too magical. It's TypeScript-native, SQL-like, and doesn't generate a big client library.

An ETag is like a fingerprint for a response.

Early return is exiting a function as soon as you have the answer, instead of setting a variable and waiting until the end.

Effect is a TypeScript library that makes your code describe WHAT to do instead of HOW to do it. Errors become typed. Dependencies become explicit.

Elysia is a Bun-first web framework that's obsessed with speed and developer experience.

An endpoint is a specific URL that your API listens on for requests.

An entity is a domain object with a unique identity that persists over time.

An entity is an object with a unique identity that persists over time. Even if a User changes their name, email, and address, they're still the same User b

An event bus is a highway for events — services publish events onto the bus, and any service that cares about that event picks it up.

Event-driven architecture means services react to things that happen instead of constantly asking 'did anything change?

Exactly-once delivery is the holy grail of messaging — every message delivered exactly one time, no more, no less.

Exponential backoff doubles the wait time between each retry. Wait 1s, then 2s, then 4s, then 8s.

Express is the most popular framework for building Node.js backends.

Fail fast means if something is going to go wrong, it should go wrong immediately — not five minutes and three API calls later.

FastAPI is a Python framework that's both blazing fast and auto-generates documentation for your API.

FastAPI's Depends is dependency injection made stupid simple. Need database access? Depends. Need the current user? Depends. Need to validate a token?

Fault injection is deliberately adding errors to your system to test how it responds. Add 500ms latency to database calls.

A feature flag is a toggle that lets you turn features on or off without deploying new code.

Feature flags are like light switches for your code. You deploy new features turned OFF, then flip the switch for 1% of users, then 10%, then everyone. If

Feature toggles on the backend let you turn features on or off without redeploying. Ship the code to production, but keep it hidden behind a flag.

Fiber is a Go framework designed to feel like Express.js. If you're a Node developer moving to Go, Fiber is your comfort blanket.

Fire and forget is sending a message or request without waiting for a response — like mailing a letter without tracking.

Five nines means 99.999% uptime — 5.26 minutes of allowed downtime per year. The SLA everyone promises and almost nobody hits.

Fixed window rate limiting counts requests in fixed time blocks (e.g., per minute). Simple: reset the counter every 60 seconds. The catch?

Flask is the lightweight Python web framework — the 'just enough' option. It doesn't come with an ORM, admin panel, or auth system by default.

GET is the HTTP method for reading data. You're just asking 'can I see that?' — no changes, no side effects.

Gin is a Go web framework that's basically Express but for Go developers. It's insanely fast because Go is insanely fast.

Go (or Golang) is a compiled language made by Google. It's fast like C but readable like Python.

Graceful shutdown is when your server stops accepting new requests but finishes all the in-flight ones before dying.

GraphQL is like ordering food where YOU specify exactly what you want on your plate.

The DataLoader pattern collects all the data requests that happen in a single tick of the event loop and batches them into one query.

GraphQL Directives are like special annotations that modify how your query behaves — think of them as post-it notes on your query saying 'skip this field'

GraphQL Federation lets multiple teams own different parts of the same GraphQL API.

GraphQL Fragments are reusable chunks of a query — like copy-pasting field selections without actually copy-pasting. If five different queries all need a u

GraphQL subscriptions are real-time updates pushed from the server to the client. Instead of polling 'any new messages?

Regular GraphQL: you ask, server answers once. GraphQL Subscriptions: you subscribe to a topic and the server pushes updates whenever data changes.

A guard in NestJS is a gatekeeper that decides if a request should be allowed through. Auth guards check if you're logged in.

A guard is a checkpoint that decides whether a request should proceed or be rejected — like a bouncer with a guest list. It runs before the route handler a

A guard clause is an early return at the top of a function that handles edge cases immediately — like a bouncer at a club. 'No ID? You're out. Under 21?

Gunicorn (Green Unicorn) is the battle-tested Python HTTP server that's been running production apps since forever.

HATEOAS is the REST principle that nobody actually follows.

An HTTP hook is an event-driven callback from an AI tool — it POSTs to your URL when something happens, no polling required.

Hapi is a Node.js framework built by Walmart's engineering team because Express wasn't enterprise-y enough for them.

A health endpoint is a simple URL (usually /health or /healthz) that returns 'I'm alive and everything's fine' or 'something's broken.

Hono is the new kid on the block for Node.js backends — ultra-fast, tiny, and designed to work on edge runtimes (Cloudflare Workers, Deno).

Hoppscotch is what happens when someone says 'what if Postman just lived in your browser tab?' It's fast, open-source, and has no login requirement.

The hot path is the code that runs the most — the fast lane of your application.

Hot reload updates your running app when you change code without restarting the whole server. Edit a file, save, and see the change instantly.

Idempotency means doing the same thing twice gives you the same result as doing it once.

An idempotency key is a unique ID you attach to a request so the server knows if it's a duplicate.

The inbox pattern is the receiving side of the outbox pattern. When a message arrives, you write it to an inbox table first, then process it.

An init container runs before your main app container starts.

Insomnia is what a lot of developers switched to when Postman required mandatory cloud sync and login.

An interceptor catches requests and responses on the way in and out, letting you transform them.

JSON is the universal language the internet uses to pass data around. It looks like a JavaScript object — curly braces, key-value pairs.

A JWT is a special kind of token that contains information inside it. It has three parts: a header, a payload (with your user ID, role, etc.

Java is one of the most widely used languages in enterprise software. It's verbose but extremely robust.

Jitter adds randomness to retry delays so all your clients don't retry at the exact same time.

A job queue is a to-do list for your server.

Keyset pagination is cursor-based pagination's more explicit cousin. Instead of an opaque cursor, you use actual column values (like 'give me everything wi

A kill switch is a way to instantly disable a feature in production without deploying new code. Something breaks?

Knex is a SQL query builder for Node.js that's like writing SQL with training wheels.

Koa is Express's slimmer, more modern sibling — made by the same team. It's lighter with better async/await support out of the box.

Laravel is the elegant PHP framework that made PHP developers feel good about themselves again.

A leaky bucket processes requests at a fixed rate, like water dripping from a bucket. No matter how fast requests pour in, they come out at a steady drip.

A liveness probe is Kubernetes repeatedly poking your app and asking 'are you still alive?

Load shedding is intentionally dropping some requests when your server is overwhelmed so it can keep serving the rest.

Long polling is a hack to fake real-time updates before WebSocket existed. Your client asks 'any new messages?

Materialized views cache query results but eventually go stale. Refreshing them re-runs the query and updates the cache.

Memcached is Redis's simpler sibling — an in-memory cache that's great at one thing: storing key-value pairs really fast.

Message acknowledgment is telling the queue 'I got this, you can delete it now.' Without acking, the queue keeps the message and might redeliver it.

Microservices is an architecture where instead of one big app, you have many tiny apps that each do one thing.

Middleware is like a security checkpoint at an airport.

A middleware chain is a series of functions that requests pass through, one after another, like an assembly line.

Mongoose is what brings order to MongoDB's chaos.

Monkey patching is changing how existing code works at runtime — reaching into a library or framework and modifying its behavior without touching the sourc...

A monolith is one big application that does everything. User management, payments, emails, notifications — all in the same codebase, deployed together.

The N+1 problem is when your code makes 1 query to get a list of things, then N more queries to get related data for each thing.

NATS is the text message of messaging systems — super fast, super simple, no fluff. While Kafka is hauling freight trains and RabbitMQ is sorting mail, NAT

NestJS is Node.js with structure. Plain Express can get messy in large projects.

Node.js lets you run JavaScript on the server — not just in the browser. Before Node.js, JavaScript was trapped in the browser.

Nodemon watches your files and restarts your server every time you save.

A null pointer exception (NPE) is what happens when your code tries to use something that doesn't exist — like calling a method on null.

OAuth is the system behind 'Login with Google.' Instead of making a new account, you let Google vouch for you.

OAuth2 is the updated version of OAuth that everyone actually uses today.

An ORM is like a translator between your code and your database. Instead of writing scary SQL, you just write normal code like `User.

Offset pagination is the classic 'skip X rows and give me the next Y rows' approach. Page 3 of 20 results means skip 40 rows and give me 20.

OpenAPI is a standard way to describe your REST API in a YAML or JSON file.

OpenTelemetry is a standard for collecting telemetry data (traces, metrics, logs) from your applications — without being locked into any specific monitorin...

PHP is a server-side language that powers a huge chunk of the internet — WordPress runs on PHP, and WordPress runs about 40% of all websites.

PM2 is the most popular process manager for Node.js.

POST is the HTTP method for creating new things. When you submit a form, sign up, or upload a file — that's a POST.

PUT replaces an entire resource with new data. It's like taking a whole document, throwing it away, and replacing it with a new version.

Pagination is splitting a huge list of results into pages.

A Payment Intent is Stripe's way of tracking a payment from 'I want to pay' to 'money received.' It's like a tracking number for a package, but for money.

Phoenix is an Elixir web framework that handles millions of connections like it's nothing.

The pipeline pattern processes data through a series of stages, where each stage transforms the data and passes it to the next.

Plugin architecture is building your app so features can be added, removed, or swapped without changing the core.

A poison message is a message that crashes your consumer every time it tries to process it.

Postman is the GUI way to talk to APIs. Instead of crafting curl commands, you have a nice interface where you set the URL, headers, body, and hit Send.

A priority queue is a job queue with a VIP lane. High-priority tasks jump ahead of low-priority ones. Password reset emails? High priority.

Prisma is the ORM that made TypeScript developers actually enjoy working with databases.

Pydantic is Python's strict bouncer at the data nightclub.

Python is a programming language famous for being super readable — almost like writing in English.

A query builder lets you build database queries by chaining methods instead of writing raw SQL. It's like assembling a sentence with Lego blocks — `.

REST is a set of rules for how APIs should behave. Think of it as the etiquette guide for servers and clients talking to each other.

The REST Maturity Model is a scorecard for how 'RESTful' your API actually is, from Level 0 (you're basically using HTTP as a tunnel) to Level 3 (full hype

REST gives you fixed endpoints that return fixed data shapes. GraphQL gives you one endpoint where you ask for exactly what you need.

RESTful just means 'follows the REST rules properly.' It's like saying someone is 'lawful' — they play by the agreed-upon rules.

If Kafka is the massive freight train, RabbitMQ is the smart postal worker who knows exactly which mailbox each letter goes to. It's great at routing messa

Rails (Ruby on Rails) is the framework that popularized the idea of 'convention over configuration' — instead of configuring everything, it has smart defau...

A rate limiter controls how many requests someone can make to your API in a given time window. It's the bouncer who says 'you've had enough — come back in

Rate limiter middleware is the bouncer that stops users from hammering your API too fast. '100 requests per minute, buddy. Come back in 30 seconds.

Rate limiting is like a bouncer who says 'you can come in 100 times per hour, then you wait.

A readiness probe tells Kubernetes 'I'm ready to receive traffic.

Redis is an incredibly fast database that lives entirely in memory (RAM). It's used as a cache, a session store, and a message queue.

If Swagger UI is the API documentation you use to test things, Redoc is the API documentation you show to customers.

The request lifecycle is the journey your HTTP request takes from the moment it hits the server to when a response goes back.

Request tracing follows a request's entire journey through your system, recording every service it touches and how long each step takes.

Request validation is checking that incoming data makes sense before you do anything with it. Is the email actually an email?

A resolver is a function that fetches the data for a single field in a GraphQL query. When you ask for user.

Response caching is saving API responses so you don't have to recalculate them every time.

Response streaming is sending data to the client bit by bit instead of all at once.

Retry with backoff means trying again when something fails, but waiting longer between each attempt. First retry: wait 1 second. Second: 2 seconds.

The Richardson Maturity Model is just the formal name for the REST Maturity Model — named after Leonard Richardson who defined the four levels. It's the sa

A route is like a road sign that tells incoming requests where to go.

The router is the traffic cop of your backend.

Ruby is a programming language designed to make developers happy. Its syntax is elegant and readable.

Rust is a compiled systems programming language obsessed with memory safety.

SQLAlchemy is Python's most powerful ORM — it's the Swiss Army knife of talking to databases.

SSE is just the abbreviation for Server-Sent Events. Same thing — the server streams updates to you over a persistent connection.

A scheduled task is just a cron job with a friendlier name. It's any piece of code that runs automatically at a set time or interval.

Think of it as the dictionary police for your data. Every message that flows through your system has to be registered in the Schema Registry first, like ge

A segfault (segmentation fault) is what happens when a program tries to access memory it's not allowed to touch — like trying to walk into someone else's h...

Serialization is turning a complex object in your code (like a User with methods and nested data) into a flat format that can be sent over the internet, li...

A server is just a computer that waits around all day answering questions.

A server action is a function that lives on the server but you can call it directly from your frontend component like it's a regular function.

Server middleware is code that runs between receiving a request and sending a response.

Server-Sent Events (SSE) is like subscribing to a news feed from the server.

Service discovery is how microservices find each other without hardcoding addresses.

Shadow traffic sends a copy of real production requests to a new service version without affecting users.

Sliding window rate limiting counts requests in a moving time window.

Sliding window rate limiting counts requests in a moving time window instead of fixed buckets. With fixed windows, you could make 100 requests at 11:59 and

Code that runs on a blockchain — once deployed, nobody can change it (which is either amazing or terrifying).

Socket.io is WebSocket with training wheels.

The specification pattern turns business rules into reusable, composable objects.

Spring (specifically Spring Boot) is the heavyweight champion of Java backend frameworks. Enterprise companies trust it to handle serious workloads.

A startup probe gives slow-starting apps time to boot without Kubernetes killing them. Some apps need 60 seconds to load ML models or warm caches.

Stripe API is the gold standard of payment APIs — it's so well-designed that other companies use it as a template for their own APIs. It handles credit car

Stripe Webhooks are Stripe's way of tapping you on the shoulder and saying 'hey, something happened with that payment.' Instead of constantly asking 'is it

Swagger is the old name for OpenAPI, plus the suite of tools around it.

Swagger UI reads your OpenAPI/Swagger spec file and turns it into a web page where users can browse endpoints and hit 'Try it out' to actually call your AP...

Throttling is like rate limiting's cousin — instead of blocking requests outright, it slows them down.

The timeout pattern is setting a deadline for operations. If a database query or API call takes too long, cancel it and return an error.

A token bucket is a rate limiting algorithm. Imagine a bucket that fills with tokens at a steady rate. Each request costs one token.

A unit of work tracks all database changes during a business operation and commits them as a single transaction.

Uvicorn is the lightning-fast ASGI server that runs your FastAPI and Starlette apps. Think of it as the engine under FastAPI's hood.

Validation is your backend's bouncer. Before any data gets into the database, the bouncer checks it: 'Is this email actually an email?

A value object is defined by its values, not its identity. Two $10 bills are interchangeable — you don't care which specific bill you have.

WSGI is the OG standard for Python web apps talking to web servers. It's been around since 2003 and it's how Django and Flask work under the hood.

The idea that the next internet should be decentralized — owned by users, not big companies.

A webhook receiver is an endpoint in your app that other services call when something happens. Instead of constantly asking Stripe 'any new payments?', Str

A way for one app to automatically notify another when something happens. Instead of constantly asking 'did anything change?

A worker is a background process that picks up jobs from a queue and does the heavy lifting.

Worker Threads let Node.js actually use more than one CPU core. Normally Node is single-threaded — it can only do one heavy calculation at a time.

A wrapper is code that wraps around other code to give it a nicer, simpler, or different interface — like putting a phone case on a phone.

XML is like JSON's older, more verbose cousin. Instead of curly braces, it uses opening and closing tags like HTML.

Zod is a TypeScript library for validating data at runtime. TypeScript types disappear when your code runs — they only exist at compile time.

A zombie process is a process that's dead but won't go away — it's finished executing but still shows up in the process table because its parent never coll...

gRPC is like REST but on steroids and speaking a secret language only computers understand.

tRPC lets you call your backend functions directly from the frontend with full TypeScript type safety — no REST endpoints, no API schema, no code generatio...