What is a ménage à trois?
A ménage à trois is a French phrase — literally 'household of three' — for a sexual arrangement involving three people, commonly a threesome. In the lifestyle it usually means a consensual threesome, often a couple plus a third (a 'unicorn' when that third is a single woman), with everyone's enthusiastic agreement.
Ménage à trois is a French term that translates literally as 'household of three.' Historically it described a domestic arrangement where three people lived together in a relationship; in everyday modern use it most often means a threesome — three people involved sexually at once.
In the lifestyle, a ménage à trois is simply a consensual threesome. A very common form is a committed couple inviting a third person to join them. When that third is a single woman who enjoys being with couples, she is often called a 'unicorn.' Configurations are usually described with shorthand like MFM (two men, one woman) or FMF (two women, one man), and those letters describe who is present rather than which interactions anyone has agreed to.
As with any lifestyle activity, the foundation is enthusiastic consent from all three people, clear communication about boundaries beforehand, and respect — the third person is an equal participant with full veto power, not an accessory to a pre-written script, and the couple's own check-in habits and safer-sex expectations should be shared plainly before meeting in a public setting.
When meeting online, couples and singles alike benefit from platforms where each adult completes an automated government-ID and biometric liveness check (see /legal/privacy) so nobody is guessing whether both halves of a couple are real people. For the related terms and dynamics, see the JoinTheSwing glossary and the answers on unicorns, throuples, and the lifestyle generally.