What is First Input Delay (FID)?
First Input Delay (FID) is a Core Web Vitals metric that Google uses to measure the responsiveness of a webpage. This is the time between the moment a user clicks on a button or link on a page and when the page actually begins processing it.
The First Input Delay, sometimes called input latency or input delay, is measured in milliseconds. You should ensure that it stays below 100 milliseconds.
Google plans to replace the First Input Delay with the Interaction to Next Paint (INP) in March 2024.