What is the First Input Delay?

First Input Delay is a web performance metric that measures the time between a user’s first interaction with a page (such as clicking a button or link) and the browser’s response to that action. It reflects how responsive and interactive a website feels to users. 

A low FID indicates a smooth experience, while higher delays suggest lag or poor optimization. FID is one of Google’s Core Web Vitals, which also impacts SEO. Optimizing code, reducing JavaScript execution, and improving server response time can help lower FID and enhance user experience.