These aren't as common as other three way combinations, and you usually see the two women taking turns pleasuring the man through hand jobs and oral sex, and sometimes even vaginal sex and anal sex.
NOTE: This can also refer to two women having lesbian sex, however the former is more commonly used.
Male 2: "Yeah, they're pretty fine."
Male 1: "I'm gonna go ask them if they want to have a DOUBLE KITTY BED PARTY!"
Male 2: "Good luck with that, haha."