Common Gateway Interface

Common Gateway Interface (CGI) is a standard for exchanging request data between a web server and an external program, which returns a response the server sends to a client.

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CGI environment variables: Variables a web server sets to pass request metadata, such as the request method and query string, to a CGI program. They carry request details into the external program without embedding them in its command-line arguments.
NCSA HTTPd: An early web server developed at the National Center for Supercomputing Applications. Its server extensions helped establish the CGI conventions used by early websites.
Web form: A web page interface that collects user input and submits it to a server. A CGI program can process submitted fields and generate a result page.
FastCGI: A protocol that lets web servers communicate with persistent application processes instead of starting one per request. It retains CGI’s separation while avoiding repeated process creation.
Standard input: The default input stream from which a program reads data supplied by its execution environment. CGI servers commonly send the body of a POST request to the program through this stream.
Rob McCool: A software developer associated with the creation of NCSA HTTPd and early CGI conventions. His work on NCSA HTTPd helped bring CGI into early Web practice.
Guestbook: A website feature that lets visitors post messages for later visitors to read. CGI scripts commonly stored submitted messages and rendered them as a page.
Server API: An interface that lets application code run within a web server’s process. Unlike traditional CGI, server APIs can avoid launching a separate process for each request.
Standard output: The default output stream to which a program writes data intended for its environment. A CGI program writes response headers and content here for the server to relay.
World Wide Web: A system of interlinked resources accessed over the Internet using web technologies. CGI developed as a way to make early web pages respond dynamically to requests.