Oracle Database Discussions

I am kinda new at oracle databases and i have one question. It is more theoretical.

I saw in Toad 4 Oracle that sessions that are running has osuser. I am wondering where this osuser is set. I looked if it has anything to do with jobs, but dont think so.

I browsed the web but did not find anything. The only thing i gound was that this user was set at instalation and to the user that is running oracle processes. But in my case that cant be true bbeacause users are different.

Any help is greatly appreciated.