Caching server:

A caching server is employed when you want to restrict your number of accesses to the Internet. There are many reasons to consider doing this. Basically, a caching server sits between the client computer and the server that would normally fulfill a client’s request. Once the client’s request is sent, it is intercepted by the caching server. The caching server maintains a library of files that have been requested in the recent past by users on the network. If the caching server has the requested information in its cache, the server returns the information without going out to the Internet.
Storing often-used information locally is a good way to reduce overall traffic to and from the Internet. A caching server does not restrict information flow. Instead, it makes a copy of requested information, so that frequently requested items can be served locally, instead of from the original Internet source. Caching servers can also be connected in a hierarchy so if the local cache does not have the information, it can pass the request to nearby caching servers that might also contain the desired files.