CDN stands for content delivery network, and the point is distance: keep common files close to the people asking for them.
Think about a company that ships the same brochure to clients nationwide. If every copy ships from one office in Dallas, far-away people wait longer. Keep stacks in regional offices and the nearest one sends it faster. A CDN is that regional-office system for web files. It’s not the same as the cloud (the broad idea of computing on someone else’s infrastructure); a CDN is specifically about delivering content from many locations instead of one origin.
How it shows up
A web page needs images, fonts, scripts, and other files. Without a CDN, those come from the site’s main server. With one, copies are stored around the network and served from a location near you, which improves latency, the time a request takes to go out and come back. A CDN depends on caching: it serves saved copies until they expire, which is why CDN problems look like cache problems (you updated a file but someone still sees the old one). DNS can sit in the routing path too, sending visitors to the best nearby location. For static sites and glossaries, this matters because much of the public web is just files delivered quickly.
Why you care
You don’t choose a CDN because it sounds technical. You choose it because slow pages cost attention. A client clicking a glossary entry or a portal shouldn’t feel the site dragging. The question is simple: are we making every visitor walk back to one office, or serving common files from the nearest good location?