A content delivery network, or CDN, is one of those infrastructure terms that sounds far more complex than the idea behind it. At heart, a CDN solves a physical problem: data takes time to travel, and the further your server is from a user, the slower everything feels. The solution is to keep copies of your content much closer to people.
Once you see it as "copies near the user", the rest follows naturally.
The problem of distance
Even at the speed of light, information takes measurable time to cross the world, and each round trip between a user and a distant server adds delay. A visitor on the other side of the planet from your single server experiences every request as a long journey. For a page made of many files, those journeys add up into noticeable sluggishness.
You cannot beat physics, but you can shorten the distance the data has to travel — which is exactly what a CDN does.
How a CDN helps
A CDN maintains a network of servers spread across many locations. It stores copies of your static content — images, scripts, styles and more — on these distributed servers, and serves each user from one physically near them. The result is shorter round trips, faster loads, and less load on your origin server, since the nearby copies handle much of the traffic.
It also adds resilience: with content served from many places, a spike in traffic or a problem in one region is far less likely to take everything down.
What to put on it
CDNs are ideal for content that does not change per user — the static assets that make up most of a page’s weight. Dynamic, personalised responses are handled differently, though modern edge platforms increasingly blur that line by running logic close to users too.
For most sites, putting static assets behind a CDN is one of the highest-impact, lowest-effort performance wins available. The concept is humble — copies closer to people — but the effect on perceived speed is large.