It tells you on the page you linked to, if you read the description.
Purposes for inbound connections that Tor handles.
OR traffic we're relaying as a member of the network (torrc's ORPort and ORListenAddress)
DIR mirroring for tor descriptor content (torrc's DirPort and DirListenAddress)
SOCKS client traffic we're sending over Tor (torrc's SocksPort and SocksListenAddress)
TRANS transparent proxy handling (torrc's TransPort and TransListenAddress)
NATD forwarding for ipfw NATD connections (torrc's NatdPort and NatdListenAddress)
DNS DNS lookups for our traffic (torrc's DNSPort and DNSListenAddress)
CONTROL controller applications (torrc's ControlPort and ControlListenAddress)
As can be discovered through the link you provided, where it states:
listener_type (stem.control.Listener) -- connection type being handled by the ports we return
default (object) -- response if the query fails