Hello PA and BDO Team. During registration we need to provide name. Where is that name used? Or is it only used for PA account?

No clue why you put this under off-topic.
But I assume it might have to do with verification? 

The name is just for your own. Only you will see that name.
I'm not sure if they actually implied they wanted your real name in case of future situations like requesting email transfers or regaining access to your lost account where they would ask for ID verification that should match this name or something.

I just entered my nickname, and that worked fine.

Thats what i did, entered my nick but because i thought it was to enter my nick not my real name, assuming things. Well... it works.

Pick any name you want your account to be called. It doesn't matter. :> There will probably be an option for the account name you pick to be used for a username login instead of your email for the Pearl Abyss launcher.

There is no statement about which name you have to enter during the registration.

But you have to select your correct region and enter your correct birthdate, if you do not provide the correct infos, they can block your account.