Lazy loading is a performance optimization technique where images and other media are loaded only when they are needed — typically when they come into the user's viewport (the visible area of the browser window). Instead of downloading every image on a page when it first loads, the browser waits until the user scrolls near an image before fetching it. This saves bandwidth, reduces initial page load time, and improves the user experience, especially on image-heavy pages like photo grids and news feeds.