The term 'black music' is used when someone is referring to 'urban' or 'street' music. To substitute the word 'street' for the word 'black' is degrading and suggests that the street is a black persons place.
Some people say the term means music that originated from African Americans but the definition doesn't fit because it doesn't encompass
UK Garage, Grime, Dubstep etc. which are all thought of as
Black Music styles. Similarly,
Rock'n'Roll is not thought of as a Black Music style dispite its origins.