A girl or tranny that stuffs her bra to have or make her tits appear larger.
My brother's flat chested girlfiend doesn't know that I know about her secret titties.
A girl's boobs that are so big that they go into her armpits when she lays down. Then her boobs smell like her secret deodorant.
"Yeah, so how was it?"
"Omg. She had secret titties!"
"She had what?!"
"Her tits got caught in her arm pit when she layed down and it freaking smelled like her deodorant!"