Perplexity
ELI5 — The Vibe Check
Perplexity (the metric) measures how 'surprised' a language model is by text — lower perplexity means the model predicted the text well. Perplexity (the company) is an AI-powered search engine that gives you direct answers with citations instead of a list of blue links. It's like Google and ChatGPT had a baby that actually cites its sources.
Real Talk
In NLP, perplexity is a metric for evaluating language models, defined as the exponentiated average negative log-likelihood of a text. Lower perplexity indicates better prediction. Perplexity AI is also a company that built an AI-powered answer engine combining web search with LLM synthesis, providing sourced answers to queries as an alternative to traditional search engines.
When You'll Hear This
"The fine-tuned model's perplexity dropped from 15 to 8." / "I use Perplexity instead of Google for research questions."
Related Terms
AI (Artificial Intelligence)
AI is when you teach a computer to do stuff that normally needs a human brain — like recognizing cats, translating languages, or writing code for you.
Evaluation
Evaluation in AI is figuring out if your model actually works — not just on test data, but in the real world.
LLM (Large Language Model)
An LLM is a humongous AI that read basically the entire internet and learned to predict what words come next, really really well.
Loss Function
The loss function is the AI's score of how badly it's doing.