Interaction to Next Paint (INP) measures the time between a user interaction and visible changes on the screen, focusing on webpage responsiveness. In contrast, First Input Delay (FID) measures the time until the browser responds to the first interaction. While INP considers overall interactivity, FID highlights delays caused by JavaScript execution. Understanding both metrics helps developers enhance user experience by ensuring quick, responsive interactions on their websites.
For more detail read a blog at : https://www.algosaga.com/blog/inp-vs-fid/