First Input Delay (FID), a Core Web Vitals metric established by Google, First input delay (FID) gauges how long it takes a user to engage with your website for the first time. (clicking a link, tapping a button, or using a unique JavaScript control).
Given that it requires user input, this metric is challenging to quantify, and FDI is an important point to consider for a website as it impacts a site's organic ranking.