Definition 1: A term used to call upon close friends.
Definition 2: Derived from the word 'negro', used by slave-owners in the 17th, 18th and 19th centuries, nigger is a racial slur that often when used by members of a non-black race can cause racial divides.
Whilst once used as a racial slur and sometimes still used as a racial slur by racist bigots, the 'n-word' is more commonly used by black people to refer to friends and 'homies'. As a result it is advised that members of non-black communities and races do NOT use this word in case people misinterpret usage as the second definition.
Until the second definition is no longer used the n-word lives in a grey area of both being a term of endearment and being a racial slur, thus it is advised non-black people do not use the word in public.
Example 1 (Definition 1):
You: "Wassup my nigger."
Friend: "Yo, how's it going bro?"
Example 1 (Definition 2):
Racist: "Look at that nigger, keep away from them lot, kids."
Racist kids: *Actively avoid black people*
Racist kids: *Grow up to perpetuate racist ideals and values*