A software program that is used to contact and obtain data from a server software program on another computer, often across a great distance. Each client program is designed to work with one or more specific kinds of server programs, and each server requires a specific kind of client. For example, an e-mail client would connect to an e-mail server to send and receive e-mail messages.

Client is a part of client-server architecture - a network architecture in which each computer or process on the network is either a client or a server. Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers ). Clients are PCs or workstations on which users run applications. Clients rely on servers for resources, such as files, devices, and even processing power.

Another type of network architecture is known as a peer-to-peer architecture because each node has equivalent responsibilities. Both client/server and peer-to-peer architectures are widely used, and each has unique advantages and disadvantages.

By not being constantly logged on (as a terminal would be logged on to a host computer) a client/server system can efficiently deal with many "clients" and doesn't waste computer cycles on an idle connection.