Polygamy refers to the practice of having more than one spouse at the same time. It can include both polygyny (one man having multiple wives) and polyandry (one woman having multiple husbands).
Related terms
Monogamy: The practice or state of being married to only one person at a time.
Bigamy: The act of marrying one person while still being legally married to another person.
Cohabitation: Living together as partners without being legally married; often used when referring to unmarried couples who live together.