Question : What the FUCK is a Holla-Back Girl?

What in the world is a Holla Back Girl?
Fuck that. I feel like that shit needs to be spelled Holla Back Gurl.
I hate Gwen Stafani and her Harafuku or whatever the hell they call it.
How do you go from Don’t Speak to Holla Back Girl and Sweet Escape?

If anyone can define Holla Back Girl to a ignorant mo’fucka like me, I’ll be grateful.