A word used to describe a person who is close to you, like a friend (or enemy). The context is what gives it meaning. The race is irrelevant as long as you know the people you are saying it to and they cool with it then you good. Unless they ain't then be ready for the consequences of using a politically charged and racial slur.
Person 1: Only real niggas know when it's coo to say nigga, right playa?
Person 2: Nigga, do I know you?
Person 1: (*gets layed out*)