Common Gateway Interface (CGI) is a standard protocol that allows web servers to execute external programs, often scripts, to generate dynamic web content. When a user submits a form or requests a specific resource, the web server uses CGI to run a designated program, which processes the input and returns output (such as HTML) to the user's browser. CGI scripts can be written in various programming languages, including Perl, Python, and Bash. While CGI enabled early dynamic websites and device management interfaces, it has security vulnerabilities if not properly configured, such as allowing unauthorized code execution. Modern web development often uses more secure alternatives, but CGI remains relevant in certain legacy systems.