Oracle Network Administration - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 213

SERVICE_NAMES should be set to global database name, in
our case it is Takveen.
Creating Net Service Name (or creating tnsnames.ora file)
Since now we have created the listener.ora file and started the
listener process. Next thing we will do is to create the Net
Service Name on this machine. Net Service Name is basically a
short & easy to remember name for a long set of parameters that
helps client applications to connect to server it includes host
name, protocol, port, instance name etc.
Select the “Service Naming” item in the tree on the left pane of
ONM and click the “+” sign to add the Net Service Name. In the
popped up window write the Net Service Name as “fan”. Now
we are going to define what the word “fan” means on this
machine by clicking “Next” button.
Figure 8-15: tnsnames.ora file resolves Net Service Name. Net Service
Name is basically the alias given to the set of TCP/IP required
connection parameters that can lead MS Access, SQL*Plus etc. to the
Oracle Server.