a service name is devided into 2:
1) the unique identifier of a service provider on a client machine. i.e service
DB1( ADDRESS = ....
CONNECT_DATA = (SID = ...))

this service is your connection to the remote database from a client.

2) on windows nt a service is the component responsible for the Oracle Instance (OracleServiceXXXX)
and for the database (OracleStartXXXX)