Sexual intercourse between three people, usually hotter when three girls.
After hanging up on a Skype call, a threesum is usually what partakes as a nighttime activity
by iMindfreak October 30, 2011
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Sexual Intercourse involving a male and 2 women.

intercourse involving 2 males and 1 women is a train.
The crowd began to advance upon the Threesum, and Omally was in the vanguard. By then the Threesum was already past its prime.
by catniporangejuice March 22, 2022
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Day when a girl gets tagged teamed by two males
National threesum day is the hottest
by ChronikGodz April 12, 2019
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