A 'French' term typically defining a sexual liason between three persons, involving three people
engaged in sexual intimacy or
sexual congress. Three people having
sexual relations with one another either randomly, such as on a one-time occassion, or regularly as long-term lovers. Three people having sex together, typically at the same time in the same bed.
A favorite fantasy of men- that of being
in bed with two women instead of just one- but women also imagine bedding for sexual purposes with two men. Such is also known well enough between three lesbian women, or between three
homosexual men. As long as three people are intimately/sexually
involved, it is a 'manage-a-trois'.