isr.co.ro : glossary Client A program that makes use of a service provided by the network or larger system--such as an e-mail client program that lets you send or receive e-mail on a network or the Internet. Clients are usually paired with "server" programs running on a network "host" or mainframe computer, but a single server can be designed to accommodate a range of clients, or vice versa. In most systems, the client program does the user-interface tasks, such as formatting the display screen and receiving keystrokes and mouse clicks, while the server does the heavy database access and communication with other servers.