First Contentful Paint, or FCP, marks the moment the browser paints the very first piece of DOM content to the screen, text, an image, a background color, anything visible, after a page starts loading. It's the point where a blank white screen finally becomes something.
FCP matters because a blank screen is where visitors decide a page is broken or too slow and leave before anything even has a chance to load. Even a page that will eventually be fast can lose visitors at this exact moment if nothing appears for a couple of seconds, since there's no visible signal that anything is happening at all. It's an early, coarse signal though, not a complete picture of speed, since a page can paint something quickly (a header, a loading skeleton) while the content the visitor actually came for takes much longer, which is why FCP is usually read alongside Largest Contentful Paint, the metric that tracks when the main content specifically becomes visible.
