What is a CGI program?

The input to the CGI program is represented by the data supplied by the user in the form, and the output is a web page, returned to the browser.

Such a program can perform a variety of tasks, like:

Database queries

the form contains a query; the CGI program will perform the query on a local or remote database, it will format the output and send it back to the client

Data entry

The form contains data to be inserted in a database that can reside either on the web site or on another machine, connected in an intranet/extranet or isolated (in this last case, the database will be updated periodically. This way, it is possible to build procedures for electronic commerce (i.e.: for collecting and processing orders).