CDN
In plain terms
A global network of servers that delivers content from a location near the user.
Going deeper
A Content Delivery Network caches copies of files (images, scripts, video) at edge locations worldwide, so users download from a nearby server. This cuts latency and offloads the origin.
Under the hood
Caches based on TTLs and cache headers; cache invalidation and dynamic-content acceleration are the hard parts, and edge compute now runs logic at PoPs.
Examples
Cloudflare, Akamai, AWS CloudFront, Fastly, caching images/JS/CSS globally.
Think of it like...
Like a popular book stocked in local libraries everywhere instead of one central archive, so everyone has a short trip to borrow it.