Adultery (anglicised from Latin adulterium) is extramarital sex that is considered objectionable on social, religious, moral, or legal grounds.
Though what sexual activities constitute adultery varies, as well as the social, religious, and legal consequences, the concept exists in many cultures and is similar in Christianity, Islam, and Judaism.
In countries where adultery is a criminal offense, punishments range from fines to caning and even capital punishment.
Since the 20th century, criminal laws against adultery have become controversial, with international organizations calling for their abolition, especially in the light of several high-profile stoning cases that have occurred in some countries.
In Canada, though the written definition in the Divorce Act refers to extramarital relations with someone of the opposite sex, a British Columbia judge used the Civil Marriage Act in a 2005 case to grant a woman a divorce from her husband who had cheated on her with another man, which the judge felt was equal reasoning to dissolve the union.
Adultery refers to sexual relations which are not officially legitimized; for example it does not refer to having sexual intercourse with multiple partners in the case of polygamy (when a man is married to more than one wife at a time, called polygyny; or when a woman is married to more than one husband at a time, called polyandry).
In the traditional English common law, adultery was a felony.
Another tort, alienation of affection, arises when one spouse deserts the other for a third person.
A marriage in which both spouses agree ahead of time to accept sexual relations by either partner with others is sometimes referred to as an open marriage or the swinging lifestyle.