Content Delivery Network
also called CDN
A geographically distributed cache that serves content from a location near the user instead of from the origin.
The first-order benefit is latency: physics puts a floor of roughly 60 ms on a round trip between continents, and no amount of backend optimisation moves it. Serving from an edge node 20 ms away does.
The second-order benefits are frequently larger — origin offload of 90%+ for static assets, absorption of traffic spikes, and DDoS mitigation by virtue of the edge fleet's capacity.
Static assets are the easy case. The gains available on dynamic content are real but require deliberate work: caching personalised pages by segment rather than by user, using stale-while- revalidate, and having a purge mechanism that is fast and reliable enough to be trusted. Egress from origin to CDN is usually cheaper than egress to the internet, which is a cost argument as well as a performance one.