CDN is short for content delivery network. This is a network of servers that deliver a web page or web content, such as video, to a user. A CDN copies the web content to a network of servers that are dispersed at geographically different locations. When a user requests content that is part of a CDN, the CDN will redirect the request from the originating site's server to a server in the CDN that is closest to the user and deliver the cached content. The closer the CDN server is to the user geographically, the faster the content will be delivered.
So using a CDN is ideal for streaming video, especially to a geographically diverse group of viewers.
In DaCast's case, we use two CDN networks: both Akamai and EdgeCast are employed to help deliver video content globally.