CGI, in simple terms, is essentially an intermediary between the a computer script and the web site. It operates to take the information from the web page and pass it to a computer script (program) and do whatever the computer program says to do. CGI is not a computer language per se, but a common language for different computer programs to interact with the web pages (hence Common Gateway Interface).

One of the recognized, and highly used, computer program languages which uses CGI is Perl. Perl. is a high level computer language which can manipulate files, text and perform system operations with ease. Perl. scripts are highly used on the web and quite frequently you hear about a very common perl. script known as "formmail." A formmail script is essentially a computer program written in Perl. which takes information from a web page and e-mails the information to someone. This is accomplished when someone fills out a form on a web page and presses a button. The button then starts the computer program (formmail) which uses CGI to get the information from the webpage and e-mails the information. Perl. scripts have been written to do quite a lot of things on a web site and it is a very powerful language. But, it is not the only computer language which can interact with a web page. Some others are ASP, PHP, C, Python, etc.