FID (First Input Delay)

First Input Delay (FID) is a Google metric that measures the time between a user’s interaction with a page (such as clicking a link or button) and when the browser is able to respond to that interaction.

Briefly, a low FID indicates that a page is responsive and provides a smooth user experience.

First Input Delay was included in the first set of Core Web Vitals metrics, although it was later joined (and then “supplanted”) by Interaction To Next Paint, which was deemed more suitable for measuring page interactivity.