In the client–server model, server-side refers to programs and operations that run on the server. This is in contrast to client-side programs and operations which run on the client.

<World-Wide Web> Processing or content generation that is done on the web server or other server, as opposed to on the client computer where the web browser is running. An example is server-side include where one file is inserted in another before it is served, rather than, say, having the browser request the files separately and combine them using an iframe. A very common kind of server-side processing is the inclusion of data from a database in a web page. There are many software environments and technologies designed for server-side processing, e.g. CGI, ISAPI, WebObjects and ASP. The greatest advantage of server-side processing is that it is independent of the many different client software environments that exist on the Internet, chiefly different web browsers and operating systems. The disadvantage is that the user must wait for a response from the server which is a much slower form of interaction than is possible with client-side processing using, e.g., JavaScript. (2003-12-29)

In computing, a server is a piece of computer hardware or software (computer program) that provides functionality for other programs or devices, called "clients". This architecture is called the client–server model.