First Meaningful Paint, or FMP, was a Lighthouse metric that tried to measure the moment a page's primary content, the part a visitor actually came for, became visible, distinct from earlier, less meaningful paints like a header or a loading skeleton.
Google deprecated FMP from Lighthouse because the heuristic behind it, guessing which paint event counted as "meaningful" based on layout changes, turned out to be unreliable and inconsistent across different page types, sometimes flagging the wrong moment as meaningful entirely. It's been replaced by more precise, better-validated metrics: Largest Contentful Paint for when the biggest visible element appears, and Speed Index for how quickly a page's visible parts fill in overall. The underlying goal FMP was reaching for, getting a visitor to the content they actually want as fast as possible, hasn't changed; the tooling for measuring it accurately has.
