A client, in German customer, is a computer or software that retrieves specific data or services on a server. The task of the client is to transmit standardized requests to the server. The received data is displayed by the client in such a way that it is easy to read on the output device. The client fulfills a mediator function between server and user.
An example makes this palpable: A common use of a client is an e-mail client that displays received e-mails in a separate mailbox without the intermediate step via a browser.
Other application areas of clients include operating systems, web browsers, VPN clients, MMPORG role-playing games or web analytics tools. It is important that the client uses a kind of protocol to communicate with the server. Even in later applications of the client, the data generated by the user must remain retrievable. That is why they are either cached on the server side or by the client itself.