The client-server software architecture model distinguishes client systems from server systems, which communicate over a computer network.

A client-server application is a distributed system comprising both client and server software. A client software process may initiate a communication session, while the server waits for requests from any client.

Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the, such as email, web access and database access, are based on the client/server model. For example, a web browser is a client program at the user computer that may access information at any web server in the world.

The most basic type of client-server architecture employs only two types of hosts: clients and servers. This type of architecture is sometimes referred to as two-tier. It allows devices to share files and resources.

The client/server model has become one of the central ideas of network computing. Most business applications being written today use the client/server model. So do the Internet's main application protocols, such as HTTP, SMTP, Telnet, DNS, etc