https://www.urbandictionary.com/define.php?term=puppy+pile&defid=2680748

A large pile of people of mixed sexes, cuddling and or heavy petting each other, usually with clothes on, but sometimes without. Not an orgy, usually done only by people who love and/or trust each other. Not always sexual, sometimes just a physical expression of love or endearment amongst multiple participants.

Originates from the carefree innocent love and romping play that puppies indulge in before they "know better."

So Sam and Lisa were in the corner cuddling when Sarah, Mike, John, and Tanya all joined in and it turned into a real puppy pile.