Nonmonogamy is a blanket term covering several different types of interpersonal relationship in which some or all participants have multiple marital, sexual, and/or romantic partners. A blanket term is a word or phrase that is used to describe multiple groups of related things. ... Interpersonal relationships are social associations, connections, or affiliations between two or more people. ... A marriage is a relationship between or among individuals, usually recognized by civil authority and/or bound by the religious beliefs of the participants. ... This article is about the issues and phenomena pertaining to human sexual function and behavior. ... Romantic love is a form of love that is often regarded as different from mere needs driven by sexual desire, or lust. ...

Forms of nonmonogamy include:

• consensual nonmonogamy, in which a nonmonogamous relationship is formed by mutual consent of those involved
• group marriage (also termed polygynandry), in which several people form a single family unit, with all considered to be married to one another
• group sex and orgies involving more than two participants at the same time
• infidelity, in which one participant fails to comply with expectations of monogamy
• Line families, a form of group marriage intended to outlive its original members by ongoing addition of new spouses
• ménage à trois, a sexual (or sometimes domestic) arrangement involving three people
• plural marriage, a form of polygyny associated with the 19th-century Church of Jesus Christ of Latter-day Saints and with present-day splinter groups from that faith
• polyamory, in which participants have multiple romantic partners
• polyandry, in which women have multiple husbands
• PolyFamilies, similar to group marriage, but some members may not consider themselves married to all other members
• polyfidelity, in which participants have multiple partners but restrict sexual activity to within a certain group
• polygamy, a term encompassing both polygamy and polyandry
• polygyny, in which men have multiple wives
• open marriage and open relationships, in which one or both members of a committed couple are sexually active with other partners
• swinging, similar to open relationships, but commonly conducted as an organised social activity

As can be seen from this list, the Greek prefix 'poly-' (meaning 'many') is often used in naming nonmonogamous forms of relationship. In informal use such names are sometimes abbreviated to just 'poly', with the rest indicated by context. Group marriage or Circle Marriage is a form of marriage in which more than one man and more than one woman form a family unit, and all members of the marriage share parental responsibility for any children arising from the marriage. ... Peter Fendi, 1835 Group sex is sexual behaviour involving more than two participants at the same time. ... Orgy. ... In a religious context, infidelity is an absence of faith in the beliefs or teachings of a religion, such that one who lacks such faith is an infidel. ... A ménage à trois is a relationship or domestic arrangement in which three people, often a married couple and another lover, live together or are romantically or sexually involved. ... Plural marriage (also sometimes called celestial marriage or spiritual wifery) is a type of polygamy that was practiced by Joseph Smith, Jr. ... The Salt Lake Temple of The Church of Jesus Christ of Latter-day Saints is the largest attraction in the citys Temple Square. ... Start of polyamory contingent at San Francisco Pride 2004. ... This article or section does not cite its references or sources. ... PolyFamilies are polyamorous families. ... Polyfidelity, a form of polyamory, is the restricting of ones sexual activities nonpreferentially to a single group of people, each of whom follows the same rules and has sex only within the group. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... This article or section does not cite its references or sources. ... An open relationship denotes a relationship (usually between two people) in which participants are free to take other partners; where the couple making this agreement is married, it is an open marriage. ... Swinging, sometimes referred to in North America as the swinging lifestyle or simply The Lifestyle (although this simplified term is also used by people into Leather and BDSM), is non-monogamous sexual activity, treated much like any other social activity, that can be experienced as a couple. ...

Many nonmonogamous terms are flexible in definition, because they are based on criteria such as 'relationship' or 'love' that are themselves variably defined; see discussions at their respective pages for more detail on individual forms. In addition, usage creates distinctions beyond the raw definitions of the words. Thus, even though some relationships might technically be considered both polygamous and polyamorous, 'polygamy' usually signifies a codified form of multiple marriage, based on established religious teachings, while 'polyamory' is based on the preferences of the participants rather than established precedent.