Polygyny (from neo-Greek: poly - "many", and gyny - "woman or wife") is a form of marriage in which a man has two or more wives at the same time. In countries where the practice is illegal, the man is referred to as a bigamist or a polygamist. It is distinguished from relationships where a man has a sexual partner outside marriage, such as a concubine, casual sexual partner, paramour, cohabits with a married woman or other culturally but not legally recognized secondary partner. Polygyny is the most common form of polygamy; the much rarer practice of polyandry is the form of marriage in which one woman has two or more husbands at the same time.