When a lady is "entertaining" three gentlemen at the same time, ie taking it from behind, giving a blow job and having sex in the traditional manner. As all three orifices are filled, she has an "air-tight" seal, leading to the term Tupperware. I thank you.
When you store food inside Tupperware in the fridge but never eat it. You know the food is off, but don't want to open it to clean it as it'll be disgusting. You also don't want to throw it away because you don't want to lose the Tupperware itself. So you leave it in your fridge in perpetuity.