Non-monogamy is a blanket term which covers several types of interpersonal relationships in which an individual forms multiple and simultaneous sexual or romantic bonds. This can be contrasted with its opposite, monogamy, and yet may arise from the same psychology. The term has been criticized as it may evoke to imply that monogamy is the norm and that any other way of relating is somehow a deviation of that norm.
Types of non-monogamy 
Many non-monogamous terms are flexible in definition, because they are based on criteria such as 'relationship' or 'love' that are themselves variably defined. 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 social custom or established precedent.
Forms of non-monogamy include:
- infidelity, where a person has a sexual affair outside of an otherwise monogamous relationship
- casual relationship a physical and emotional relationship between two unmarried people who may have a sexual relationship
- 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
- 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
- open marriage and open relationships, in which one or both members of a committed couple may become sexually active with other partners
- polyamory, in which participants have multiple romantic partners
- Poly families, 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, in which one person in a relationship has married multiple partners
- polyandry, in which women have multiple husbands
- polygyny, in which men have multiple wives
- plural marriage, a form of polygyny associated with the Latter Day Saint movement in the 19th-century and with present-day splinter groups from that faith. It is also associated with an evangelical splinter group which advocates Christian Plural Marriage
- Relationship anarchy, which do not divide relationships of partners and non-partners, but have a more flexible approach to relationships where everything is allowed so long as everyone can accept the agreement.
- swinging, similar to open relationships, but commonly conducted as an organized social activity