CGI is an abbreviation for Common Gateway Interface. http://www.w3c.org/ is one body which proposes and approves standards for internet applications - see [quote reference] for CGI related standards.
[List other useful references - perhaps like Apache's mod_dtcl, etc.]
[I should make a point of explaining clearly that there are several distinct approaches to CGI coding with Tcl, including:
To the extent that CGI is used in the casual sense of "dynamically generated web pages, or forms handling, or Web application", there is also AOLServer, with its built-in TCL interpreter and database hooks, and nstcl, which is a TCL-only extension which has AOLServer's API to http queries and database handling, as well as a templating library.