What is Old Girl?
1.
Can be a number of things. Mostly it's the new flavor of the week, they are called this til they graduate to "Baby Momma" or "The Wife." Often times, old girl is a called this because she is kept on the DL and/or your ashamed of her.
"I think old girl put something in my drink"
Reggie: Whatchu doin tonight?
Ab: Chillin out with old girl.
2.
Your mom. Mother
my old girl asked me to pick her up somthin at da store.
3.
As above.
Very common in Australia.
See
