A hardware server is a shared computer on a network that provides services to clients. A software server is a program that provides services to client programs.
Services are provided generally over local area networks or wide area networks. A client program and server program traditionally connect by passing messages encoded using a protocol.
The most common servers on a local area network are file, name, mail, print, and fax servers. Another common example of a server is an internet-connected Web server. The minicomputers, mainframes, and super computers at data centers are also servers.