A Server is a hardware system or computer program dedicated to managing access to centralized resources or services supplied to users of the other computers on the network.
Any automated process that manages the allocation of resources to one or more client processes is a server. For example, even though file sharing requires the existence of files on a machine, it is not, itself, classified as a server. The device or program that shares these files to customers via the operating system is the server.
Servers generally offer essential programs or services across a network, either to private customers inside a large organization or to public users through the web. For example, when a term is entered into a search engine, the query is sent from the individual computer via the internet to the servers that store the applicable web pages. The results are then relayed back by the server to the computer — almost instantaneously in most cases.