A foursome is a form of group sex involving four people of any gender combination.
Types of foursomes
The level of sexual activity among the four members may very greatly. Other foursomes may involve some same sex contact, and some foursomes actively involve all four members.
Wife swapping involves two couples, usually both married heterosexual pairs, where each man swaps his wife for the other, and has sexual intercourse with her. There is usally no sexual contact between the two wives, or the two husbands. Although this act is named for married couples, it applies equally to unmarried and homosexual couples. Wife swapping is sometimes simply called "swapping" as some people find the term "wife swapping" degrading to women and implies treating them as objects.
Soft Swinging involves two couples, where either one couple has a voyeuristic role watching the other have sex, or the couples each have sex but with no sexual contact between the two pairs.
A Gangbang involves three (or more) people having sex with a fourth successively. This usually occurs with men penetrating women, but can equally apply to homosexual acts,or women penetrating men using Strap-on dildos.
The airtight seal involves vaginal sex and anal sex performed on a woman by two men in a double penetration, while the woman performs fellatio on a third man.
A quad is a romantic relationship involving four people. it is most commonly used to describe a love relationship between two couples where it takes the form of a square, in which all four people have a love relationship with each other.
While it can refer to two people independently romantically linked with two others, it usually implies that each of the four people has some kind of sexual relationship with the other three. The relationships are normally friendships though romantic. Addition of bisexual or homosexual characters adds many possible combinations of sexes, and of romantic and sexual interactions.