Shoutcast servers are radio servers.
A CDN is a content delivery network, which is "a system of computers containing copies of data, placed at various points in a network so as to maximize bandwidth for access to the data from clients throughout the network. A client accesses a copy of the data near to the client, as opposed to all clients accessing the same central server, so as to avoid bottlenecks near that server." (Wikipedia
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Basically, static files are cached on varies servers spread out geographically. When a visitor needs that file, it will pull it from the closest server, increasing your loading speed.
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