Definition: A browser metric that measures when the largest visible piece of content on a page, such as a hero image or main heading, appears for the user. It is the loading signal within Google's Core Web Vitals.
So what? It answers a simple question from the user's side of the screen: when does the main content actually show up? This makes it a useful signal for observing loading performance in real browsers.
Example: A product page where the main product photo takes four seconds to appear because it was uploaded at full resolution.
