Source : Free On-Line Dictionary of Computing

Common Gateway Interface
     
         (CGI) A {standard} for running external
        {programs} from a {World-Wide Web} {HTTP} {server}.  CGI
        specifies how to pass {arguments} to the executing program as
        part of the HTTP request.  It also defines a set of
        {environment variables}.  Commonly, the program will generate
        some {HTML} which will be passed back to the {browser} but it
        can also request {URL redirection}.
     
        CGI allows the returned HTML (or other document type) to
        depend in any arbitrary way on the request.  The CGI program
        can, for example, access information in a {database} and
        format the results as HTML.  A CGI program can be any program
        which can accept command line arguments.  {Perl} is a common
        choice for writing CGI scripts.  Some {HTTP servers} require
        CGI programs to reside in a special directory, often
        "/cgi-bin" but better servers provide ways to distinguish CGI
        programs so they can be kept in the same directories as the
        HTML files to which they are related.
     
        Whenever the server receives a CGI execution request it
        creates a new process to run the external program.  If the
        process fails to terminate for some reason, or if requests are
        received faster than the server can respond to them, the
        server may become swamped with processes.
     
        In order to improve performance, {Netscape} devised {NSAPI}
        and {Microsoft} developed the {ISAPI} standard which allow
        CGI-like tasks to run as part of the main server process, thus
        avoiding the overhead of creating a new process to handle each
        CGI invocation.
     
        Current version: 1.1.
     
        {NCSA (http://hoohoo.ncsa.uiuc.edu/cgi)}.
     
        (2002-06-03)