The CGI (Common Gateway Interface) defines a way for a web
server to interact with external content-generating programs,
which are often referred to as CGI programs or CGI scripts.
Within Tomcat, CGI support can be added when you are using
Tomcat as your HTTP server and require CGI support. Typically
this is done during development when you don't want to run a web
server like Tomcat's CGI support is largely compatible with
Apache httpd's, but there are some limitations (e.g., only one
cgi-bin directory). CGI support is implemented using the servlet
class this servlet is mapped to the URL pattern "/cgi-bin/*". By
default CGI support is disabled in Tomcat.