A ménage à trois is a domestic arrangement or committed relationship consisting of three people in polyamorous romantic or sexual relations with each other, and often dwelling together. The phrase is a loan from French meaning "household of three". Contemporary arrangements are sometimes identified as a throuple, thruple, or triad.
Postcard, c. 1910
Polyamory is the practice of, or desire for, romantic relationships with more than one partner at the same time, with the informed consent of all partners involved. People who identify as polyamorous may believe in consensual non-monogamy with a conscious management of jealousy and reject the view that sexual and relational exclusivity (monogamy) are prerequisite for deep, committed, long-term, loving relationships. Others prefer to restrict their sexual activity to only members of the group, a closed polyamorous relationship that is usually referred to as polyfidelity.
Three people in a polyamorous relationship.
Cosplay of the superhero Starfire at FanimeCon 2015
Bridgette Garozzo, spokesperson for the Polyamory Action Lobby, in May 2013