Lazy Loading
Lazy loading delays loading images and content until the visitor is about to see them.
Instead of loading every resource on a page as soon as it opens, the browser only loads what is visible on screen, then the rest as the visitor scrolls. The first paint becomes faster.
Used correctly, lazy loading directly improves Core Web Vitals. Implemented poorly, on an image visible right at opening for example, it can slow down the main render instead.