Oracle Network Administration - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 206

Creating Listener (or creating listerner.ora file)
Select the Listener item from the tree in ONM and then click the
'+' sign shown in Figure 8-6 to create the listener. In the popped
up window write the Listener Name. If you use the default name
of the listener than the Oracle Instance registers itself with the
listener dynamically and it's called dynamic service registration.
That's why we are sticking with the default name of the listener
i.e. LISTENER.
Figure 8-6: First add a listener by clicking the “+” sign.
Figure 8-7: For dynamic registration of service, use default listener
name.