A computer that delivers (serves up) Web pages. Every Web server has an IP address and possibly a domain name. For example, if you enter the URL http://www.domainname.com/index.html in your browser, this sends a request to the server whose domain name is domainname.com. The server then fetches the page named index.html and sends it to your browser.
Any computer can be turned into a Web server by installing server software and connecting the machine to the Internet. There are many Web server software applications, including public domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape and others.