Polygamy

Monogamy (Practice of being married to only one woman at a time) is the most natural form of matrimony. The spirit of exclusive relationship or individual and private ownership prevails in it, though this ownership is different from that of wealth or property. In this system the husband and wife each regard the feelings, sentiments and the sexual benefits of the other, as exclusively belonging to him or to her.
The opposites of monogamy are polygamy (Custom of having more than one wife at the same time) and sexual communism. The latter, in a sense, may also be regarded as a form of polygamy.

Adapted from the book: "Woman and Her Rights" by: "Shahid Murtaza Mutahhari