1. A derogatory term used against Africans but yet has been made popular in today's culture.
2. It can also mean a black person that is useless. Just like calling a white person a cracker or a Hispanic person a spic, i.e. all niggers are black but not all black people are niggers.
So yes, There is a difference between a black person and a nigger.
Look at the way that guy acts. He just put his people back another 1000 years (*cough* rappers *cough*). Yeah, he's behaving like a total nigger.