Intercompany invoice

Hello Gurus,

What is inercompany invoice? I am very confusing , am not asking about inter company transaction that means payment made by one company instead of other company. for this we need OBYA configuration. upto this i know. Now my confusion is what is inter company invoice? for example while creating invoice in company code ABC if I enter in customer field XYZ company as customer. then it becomes intercompany invoice?pls clarify