In the South (but probably everywhere else) this term is used to describe African-American women that can't stand to see a black man with a white woman. It pisses them off to no end and it doesn't matter whether said African American woman knows this guy or if she is even interested in him. It is the simple fact alone that the female with the black man is white that makes her angry.
African American Lady- "Damn look at that motherfucker. I can't believe he would be with the white bitch. Man, fuck that!"
White lady- "Man, it's alright. Ol' girl just black and mad. She'll get over it."