Definition of tweeners:
(n) :
(informal) A tweenager.
(n) :
(informal) A person or thing that is between two categories, classes or age groups.
(n) :
(sports, chiefly basketball) A person who plays at two positions, especially if not good enough at either to be restricted to it.
(n) :
(film) A film that falls between two genres or audiences (and thus may not be easily marketed).
(n) :
(computing) A computing device that is smaller than a traditional laptop, but larger than a PDA.
(n) :
(boxing) A boxer in various newcomer weight classes whose names often contain super, light or junior.