Unofficial Girl 

Unofficial girl is a girl who is just a hook up with a guy.Nothing more than just a fuck buddy to him.Not in a relationship with the girl.

Like in Cassie and Lil Wayne's song...

And I'm tired I'm tired I'm tired of being your (your) unofficial girl unofficial girl und I'm tired I'm tired of trying(ooh but I'm still your)I'm still your unofficial girl.

Unofficial Girl by Jessica Rae{Slick} December 21, 2008

Unofficial Girlfriend 

The term unofficial girlfriend is used to describe the female partner in the relationship when neither of the people in the relationship have made it official. The term unofficial girlfriend is used to show you intend to make said girl your girlfriend at some point. If you have an unofficial girlfriend you may act and speak as if she is your girlfriend but technically she is not. Exclusivity with unofficial girlfriends is optional, unlike with official ones.

“I will ask her out eventually but for now she is my unofficial girlfriend”

Unofficial Girlfriend by Starlin Vander February 3, 2020