Definition - What does Key Party mean?
A key party is a specific kind of party held by swingers. The premise is that upon arrival, all of the male attendees place their keys in one bowl and at the end of the night their female partners select a set of keys and go home with its owner.
Kinkly explains Key Party
Key parties are generally associated with 1970s swinger culture and there is even speculation as to whether they ever actually enjoyed the popularity that many believe.
Modern swinger culture has seen a revival of the key party as a "retro" spin on the typical sex party.