INP, or Input Timing, is a metric that measures the responsiveness of a web page to user interactions. It focuses on the time between when a user initiates an interaction and when the next frame is presented with visual feedback. Good responsiveness means that the page quickly responds to user actions, providing immediate visual feedback. INP is calculated by observing all click, tap, and keyboard interactions on a page, and the final INP value is the longest interaction observed. A good threshold for INP is below 200 milliseconds, while anything above 500 milliseconds indicates poor responsiveness. INP is different from First Input Delay (FID), as it considers all interactions, not just the first one. Field data and lab testing can be used to measure and improve INP.
https://web.dev/inp/