In general, someone or something receiving a service of some kind. Within computing the term frequently refers to one element of a client/server system, typically an application, that communicates with the end-user by means of a server.
Internet
A program or computer that requests some service from a server. For example, a browser accessing Web pages from a Web server acts as a client to that server, and an FTP client asks for files to be downloaded from an FTP server. See client server computing.