CGI (Common Gateway Interface)

It is a set of rules that describe how a Web Server communicates with another piece of software on the same machine, and how the other piece of software (the “CGI program”) talks to the web server. Usually a CGI program is a small program that takes data from a web server and does something with it, like putting the content of a form into an e-mail message, or turning the data into a database query. You can often see that a CGI program is being used by seeing “cgi-bin” in a URL, but not always.