Content Delivery Networks are used to speed up sites by removing the bottleneck created by having one server provide files. These added servers are then spread out over a geographical area bringing the files closer to end users. This network could be global or regional.
Cloudflare is an example of a CDN as well as Jetpack. A popular paid CDN is AWS’s Cloudfront. These servers are called Edge servers as they are on the edge of the companies network all over.