Web Design in a Nutshell, 3rd Edition

Servers 101

A server is any computer running software that enables it to answer requests for documents and other data. The programs that request and display documents (such as a browser) are called clients . The terms server-side and client-side, in regard to such specific functions refer to which machine is doing the processing. Client-side functions happen on the user’s machine; server-side functions occur on the remote machine.

Web servers answer requests from browsers (the client program), retrieve the specified file (or execute a script), and return the document or script results. Web browsers and servers communicate via the Hypertext Transfer Protocol (HTTP).