The Common Gateway Interface (CGI) is a standard protocol for interfacing external application software with an information server – for example, a web server.

In contrast with a plain HTML document that the Web daemon retrieves is static, CGI program is executed in real-time for dynamic information output.

Generally, web servers (including Bluehost) often have a cgi-bin directory at the base of the directory tree to hold executable files called with CGI.

Implementation of CGI

An instant example on the usage of CGI quoted from NCSA.

For example, let’s say that you wanted to “hook up” your Unix database to the World Wide Web, to allow people from all over the world to query it. Basically, you need to create a CGI program that the Web daemon will execute to transmit information to the database engine, and receive the results back again and display them to the client. This is an example of a gateway, and this is where CGI, currently version 1.1, got its origins.

Does Bluehost limit CGI script usage?

No, as long as the CGI scripts are not harmful to the web servers, there’s no limitation on your CGI scripts usage at Bluehost.