Lazy loading waits to download images, video, and other heavy files until the visitor is about to see them. The first screen can arrive before the rest of the page. What is below the fold waits its turn.
It is not a cache. A cache stores a copy so the next request is faster. Lazy loading changes when the first download happens. Both support Core Web Vitals, along with a CDN and sane hosting. A PWA may cache what lazy loading deferred. Alt text still belongs on the image — delaying the file does not excuse a missing description. Responsive design decides which size to fetch. Lazy loading decides when.
A real-life example of lazy loading
An Atlanta flower shop’s catalog has dozens of bouquet photos. Without lazy loading, the phone tries to pull every image before the first row is readable. With it, that row appears, and the peonies further down wait. The shopper can already tap “Order.”
Ship the first screen, then the rest. How-to: lazy load images and front-end speed tweaks.