A server on the Internet is a computer that responds to requests for information. Servers run special software to be able to respond to requests, but any computer on the Internet can act as a server. There are several types of servers for the various types of information shared on the Internet. For example, a mail server responds to requests to send and receive e-mail messages. A news server responds to requests to view the newsgroups it stores, and a web server responds to requests to see the web pages it stores. A single computer might take several of these server roles. And it might simultaneously act as a client as well.
A client on the Internet is a computer that requests information from a server. Clients run client software. Office comes with a few Internet client programs—the Internet Explorer web browser is a client program. Outlook is an e-mail client, and Outlook Express is an e-mail and news client.