(derogatory) A woman, usually from New Jersey, characterised as loud and wearing bright clothing, far too much make-up, big hair and oversized gaudy earrings.

http://en.wiktionary.org/wiki/Jersey_girl

A girl with a certain tacky yet awesome sense of style, who loves beer and smoking cigarettes. Listens to Bon Jovi and Bruce Springstein. Loves to go "down the shore". To pass the time hangs out with her friends at the mall and drives around at night. Has a big loving heart but don't cross her because she can tell you the hell off.

http://www.urbandictionary.com/define.php

This term was coined by the "Boss" Bruce Spingsteen at the Stone Pony Club in Asbury Park New Jersey on February 10th 1971.