1. Sexual activity involving three people (threesome) regardless of gender (two men and one woman, three men, two women and one man, or three women). This is known colloquially as: club sandwich; cluster- fuck; double peptide; flesh sandwich; ménage à trois; Peter, Paul and Mary; Oreo cookie; sandwich; sausage sandwich; séance à trois; three decker; three high; three-hole activities; three-in-a-bed: three-layer cake; Three P; threesies; three-way; three-way split; three-way swing; threesome; triple shag.
ETYMOLOGY: From the French trois , three.
2. In psychiatry, a paraphilic condition in which sexuoerotic arousal and gratification are dependant upon sharing one's partner with a third party and observing them while they engage in sexual activities. When the partner is rented out, troilism is a paraphilia of the mercantile/venal type.