A site is a particular persistent instance of an application. Sites are configured in a .ini file, usually sites.ini. Here is an example sites.ini:
[site:mysite]
application = myproject#myapp
zodb_uri = zeo://localhost:8888/
This defines a site, mysite, which uses the app, myproject#myapp and connects to a ZEO server listening on port 8888 for persistence. The minimum definition for a site consists of the application to use and a URI to use to connect to a ZODB for persistence. myproject#myapp is the entry point defined earlier in the section, Applications.