A slang neologism for anything that is neither A nor B, but rather in-between. The term tweener—or more formal permutations thereof—has been used in:
A child between age 7–older than a little kid and 12–not yet a teenager
Any lesion that has histological features from opposite ends of a spectrum, as would be an adenoma with features of carcinoma, such as cellular atypia, increased mitoses, and an infiltrative pattern
The No Man’s Land between the posterior scrotum or posterior vaginal introitus and anus
A culturally confused white male adolescent or young adult who aligns himself more with blacks than his white peers and is thus shunned by both groups.
A pejorative basketball term for a player who can play two positions but isn’t well-suited for either position exclusively, and thus said to be in between