Answer:
polyandry
Explanation:
Polyandry is the form of marriage in which a woman possess two husbands at the same time. It is discouraged in modern societies but it was prevalent in ancient times where the husband has to go for business or war and the wife needs a male to protect her. Secondly, the mortality rate of men at that time was greater than women because of the frequent war, where participation of men was compulsory. Therefore, the social system allows a woman to have more than one husband.
As per the question, the contract of marriage of a woman with two husbands is called polyandry.