what is it??

As the person above said, it’s a prenuptial or premarital agreement, as far as I’m aware it means that you both agree that if you get divorced you each leave with what you had when you came into the marriage. For example; say a woman and a man got married, and before the marriage the woman owned 3 houses and the man owned 1, with a premarital agreement after the divorce the woman keeps her 3 houses and the man keeps his 1, instead of everything being split down the middle.