First Input Delay (FID) is a user-centric metric that measures the time from when a user first interacts with a page (e.g., clicks a button, taps on a link) to the time when the browser is able to respond to that interaction. FID is an important metric for evaluating the responsiveness and interactivity of a web page, particularly during the initial loading phase.
FID is part of Google’s Core Web Vitals, a set of metrics designed to help site owners understand and improve user experience on their websites. A good FID score indicates that a web page is responsive to user input, leading to a better overall user experience.