The Common Gateway Interface (CGI) is an important World Wide Web technology that allows a client (web browser) to request data from a program running on a web server. CGI specifies a standard for transferring data between the client and the program. It is a mechanism of communication between the web server and an external application whose final result of the execution are MIME objects. Applications running on the server are called CGIs.
CGI applications were one of the first practical ways to create dynamic content for web pages. In a CGI application, the web server passes client requests to an external program. The output of that program is sent to the client instead of the traditional static file.
CGI has made it possible to implement new and varied functions in web pages, so that this interface quickly became a standard, being implemented in all types of web servers.