An expression referring to a married couple having sex while their kid is at a friend's house, or at school, or a sleepover, etc.
Fish: Dude what happened?

Mike: I walked in on my parents having sex and my mom looked at me and said, "When the cat is away, the mice will come out and play."
by Alfred Miller September 27, 2009
When your significant other or parents are away for a few days and you plan with your old trustful friends to meet up.
It usually happens in a tucked away shack in the woods where wild and crazy sexual experiences occur. You smoke weed, sing songs, lots of laughs, massages, spa baths, explore various kinds of sexual pleasure, lots of dirty taboo sex which is so good you're not even allowed to think about it. It can occur between two or more groups of friends, depends on what tickles your fancy.
Sia: 'Having sex with someone you really shouldn't be having sex with can make you reach for the skies faster than Kim Jong-Un's super large heavy nuclear warhead'.
Jocelyn: 'True, when the cats are away, the mice will come out and play that's for sure'.
by patootie's girl December 23, 2017