CDN: serve from the edge, not the origin
A Content Delivery Network has hundreds of PoPs (Points of Presence) worldwide. When a user requests a file, DNS routes them to the nearest edge node (anycast or GeoDNS).
The edge node caches responses — if the file is cached, it's served in milliseconds from a nearby server. If not, it fetches from the origin server once and caches it for all future requests.