A word originally used to describe and belittle a Negro when slavery was commonplace. "Nigger" is branched from the word Negro, which is the common term to describe a member of the Negroid race, just as one can be a member of the Aryan race.
Many people, mostly Hispanic gangbangers
, become confused around this word, using it to discribe Hispanic people or people of Hispanic origins, which is NOT it's true meaning. A Hispanic person or a person of Hispanic origin is not nececarily a nigger, because being Hispanic is different from being Negroid. One can be both Hispanic and Negroid, but just because someone is Hispanic does not make him or her Negroid.
A nigger, nowadays, reffers to a trashy
Negro person. This Negro person doesn't have to be widly accepted as being trashy, but can only be concidered to deserve to be belittled by one person - the person calling them a nigger. When this term is used, it is widly frowned upon, due to it's connotative nature, and tendance to get the user knifed or assaulted by gang members that believe they can get away with anything.
It's really ironic when a Mexian gets mad at you for calling somebody a nigger, 'cause it just makes you wanna call THEM a nigger, only proving thier point; that you're a racist fuck.