GLOSSARY TERM
What is FID (First Input Delay)?
Definition
The time from a user's first interaction (click, tap, key press) to when the browser actually starts processing it. Replaced by INP as a Core Web Vital in March 2024.
Why it Matters for AI Search
FID is now historical, but the measurement still appears in older reports. If you see FID referenced in 2026, the source data is stale. Use INP for current responsiveness measurement.
Related Terms
Interaction to Next Paint (INP)CrUX (Chrome User Experience Report)TTFB (Time to First Byte)TTI (Time to Interactive)PageSpeed Insights (PSI)Lighthouse
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