Threesome
In human sexuality, a threesome is commonly understood as "a sexual interaction between three people whereby at least one engages in physical sexual behaviour with both the other individuals". The term threesome most commonly refers to sexual activity involving three participants, but it has also been used to refer to a long-term domestic relationship, such as polyamory or a ménage à trois.
A threesome is a form of group sex that typically occurs in private settings, such as spontaneous sexual activity among three friends or in the context of casual sex or a hook up. It could also take place in specific contexts or environments that allow for sex, such as swingers events, orgies, or sex parties.
Threesomes are a common element of sexual fantasy, and are commonly depicted in pornography.