In a network, the resources of computers comprising network are usually shareable. In fact, one of the main objectives of networking is to make the computing resources shareable.
Computers in a network that make their resources available for sharing are called server. Typically, Servers are very powerful computers (relative to other computers in the network). A server. is also said to be the one providing services e.g. a server can offer services for sharing files, printers, etc. In such cases the server is appropriately called a file server or a print seLver etc.
A server usually has a network operating system running on it to enable it to provide the services. This operating system could be Novel1 NetWare or Windows XP etc.