Final answer:
The form of marriage in Nepal and Tibet where one husband works on the family farm and another in the urban area for cash, thus providing a safety net for the wife, is known as fraternal polyandry.
Step-by-step explanation:
In Nepal and Tibet, the form of marriage that provides a safety net for a wife by having one husband work on the family farm, while the second one works in an urban area to earn cash money, is known as fraternal polyandry. This form of marriage is practiced by a minority of mainly rural families in Nepal and is a beneficial social strategy in places with scarce resources and dense population. It minimizes population growth and allows all the brothers to share an inheritance of land rather than dividing it, reducing household inequality and maximizing the utilization of family labor by alternating roles between farming and earning additional income in urban areas.