FOIT
ELI5 — The Vibe Check
FOIT is when your browser hides all the text until the custom font loads, like a magician making your content vanish. 'Ta-da! Your heading is... invisible for 3 seconds!' Nobody claps. Users leave. The end.
Real Talk
Flash of Invisible Text (FOIT) occurs when browsers hide text while waiting for a custom font to download. This is the default behavior in many browsers and can make content unreadable for seconds. It's mitigated with font-display: swap or optional.
When You'll Hear This
"Safari's FOIT behavior hid our entire hero section for 4 seconds on 3G" / "We eliminated FOIT by setting font-display: optional for non-critical fonts"
Related Terms
Font Optimization
Downloading an entire font family is like ordering the complete encyclopedia when you only need Volume F.
FOUT
FOUT is when your page shows up in boring system fonts and then — SURPRISE — swaps to the fancy custom font a second later.
Web Font Loading
Web font loading is the art of getting custom fonts to show up without your text doing a magic disappearing act or a jarring costume change mid-sentence.