Extramarital sexual acts not fitting this definition are not "adultery" though they may constitute "unreasonable behavior", also a ground of divorce.
The application of the term to the act appears to arise from the idea that "criminal intercourse with a married woman ...
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.
In 1707, English Lord Chief Justice John Holt stated that a man having sexual relations with another man's wife was "the highest invasion of property" and claimed, in regard to the aggrieved husband, that "a man cannot receive a higher provocation" (in a case of murder or manslaughter). 1 (1751), also equated adultery to theft writing that, "adultery is, after homicide, the most punishable of all crimes, because it is the most cruel of all thefts, and an outrage capable of inciting murders and the most deplorable excesses." Legal definitions of adultery vary.It is a non-cognizable, non-bailable criminal offence.A police officer cannot arrest a person without a warrant in a case of adultery as adultery is a non-cognizable offence.Adultery often incurred severe punishment, usually for the woman and sometimes for the man, with penalties including capital punishment, mutilation, or torture.Such punishments have gradually fallen into disfavor, especially in Western countries from the 19th century.