a server side language needs to get information from the web apge or the web browser, send it to a program that is run on the hosts's server and then the information is sent back to the browser.

as a programmer you have many options that a clien-side language can't. such as saving information on the web server for later use.

here are some programming languages that are server side:

PHP - PHP is by far the most popular
ASP
CGI