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1.
Wannabe teenagers that aren't old enough to be considered teens.

Usually girls that tart themselves up to look like whores around the age of 8-11. Absolutely horrible

Tell tale signs of being a tweenie are flip phones, big hoopy earrings and awful, awful blue eye shadow all before the age of 13.
Look around your local cinema/McDonalds for an example of a tweenie
by Your Uncle Cordelia September 19, 2006
 
2.
A girl under 13 acting like a whore. Such as reveling clothes, stupid makeup, big hoop earrings and normally thinks they're sexy or so popular.
OMG! Look It's enter name Her Skirt And Top Only Just Cover Her, She Is Such A Tweenie
by Razorblade Raver May 26, 2010
 
3.
Tweenie can be a compliment. You are considered a tweenie when you act or say something corny, hilar, silly, or cheesy. Tweenie can be referred to as someone or something/ some action.
She was such a tweenie when she started watching christmas movies before thanksgiving.
by Kirem October 10, 2010