Final answer:
Polygamy refers to the practice of having multiple spouses simultaneously and is illegal in the United States but practiced in some parts of the world. Monogamy, involving marriage to a single spouse at a time, is most common and includes same-sex marriage which is legally recognized in many countries, including the U.S.
Step-by-step explanation:
The marriage involving one person of one sex with two or more persons of the opposite sex is known as polygamy. This is a type of marital relationship where an individual has multiple spouses simultaneously. In the United States, polygamy is legally prohibited and is considered socially unacceptable.
However, this form of marriage is still practiced in some cultures and countries around the world. Generally, the instances of polygamy reported are of a polygynous nature, where a man is married to more than one woman at a time.
In contrast, monogamy is the practice of being married to only one person at a time and is the most accepted form of marriage in many societies, including the United States.
Monogamy includes both opposite-sex marriages and same-sex marriages, with the latter gaining legal recognition in the U.S. following the Supreme Court case Obergefell v. Hodges in June 2015. As of now, same-sex marriage is legal in several countries globally, reflecting an increasing acceptance of diverse forms of union.