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 someone uses butter bowls and other store bought food cantainer to transport their lunch to work or the family picnic.(country crock I can't believe it's not butter bowls)