Marriage to more than one spouse at a time.
Although the term may also refer to polyandry (marriage to more than one man) it is often used as a synonym for polygyny (marriage to more than one woman), which appears to have once been common in most of the world and is still found widely in some cultures. Polygyny seems to offer the husband increased prestige, economic stability, and sexual companionship in cultures where pregnancy and lactation dictate abstinence, while offering the wives a shared labour burden and an institutionalized role where a surplus of unmarried women might otherwise exist. The polygynous family is often fraught with bickering and sexual jealousy; to preserve harmony, one wife may be accorded seniority, and each wife and her children may have separate living quarters. Polyandry is relatively rare; in Tibet and Nepal, where brothers may marry a single woman, the practice serves to limit the number of descendants and keep limited land within the household.