Wrappers
The server or gateway invokes the application callable once for each request it receives from an HTTP client, that is directed at the application.
Currently wrappers are available for FastCGI, CGI, SCGI, AJP (using flup), twisted.web, Apache (using mod_wsgi or mod_python) and Microsoft IIS (using isapi-wsgi, PyISAPIe, or an ASP gateway).
Read more about this topic: Web Server Gateway Interface