The Collaborative International Dictionary of English v.0.48:

Tupperware \Tupperware\, Tupper ware \Tup"per ware\, n. [Trade
   name.]
   1. the collective trade name for a type of plastic
      food-storage container with a translucent bottom and a
      close-fitting lid designed to seal the container tightly.
      It is in common use in the late 20th century and early
      21st century in the U. S. It comes in a variety of shapes
      and sizes, suitable for storing a variety of items. Also
      used attributively. She saved the leftovers in a couple of
      Tupperware containers.
      [PJC]