Largest Contentful Paint (LCP) is a Core Web Vital that measures how long it takes for the largest visible content element in the viewport to fully render after a page begins loading — used as a proxy for "when does the page feel loaded to the user?" LCP tracks the largest image, video poster frame, background image via CSS, or block of text that becomes visible. Google's threshold is under 2.5 seconds for "good," 2.5–4.0 seconds for "needs improvement," and above 4.0 seconds for "poor," measured at the 75th percentile of real-user page loads from CrUX data. The dominant contributor to slow LCP on WordPress sites is an unoptimized hero image: a large, uncompressed image that isn't preloaded. Key fixes include adding fetchpriority="high" and rel="preload" to the LCP image element, serving it in WebP format, hosting on a CDN, and ensuring the image is not lazy-loaded (lazy loading delays LCP by design).
Glossary entry