A content delivery network (CDN) is a network of geographically distributed servers that accelerate the delivery of web content by caching copies closer to end users.
It's like a pizza chain having multiple locations spread across a region instead of one central location. When an order comes in for delivery, it is routed to the nearest location to shorten the delivery time.
The CDN has caching servers stationed at data centers all over the world. When a user requests content from a customer's website, the CDN automatically routes the request to the server that can deliver the content the fastest instead of the only main origin server that may be very distant. This allows for faster delivery of content to users across more locations.