What's a pre-nub (wedding contract)

So I know it's a contract regarding the marriage and usually revolves around money..

But what exactly does it mean?

I'm watching this american show called "marrying millions" which is why I'm asking..

If my husband-to-be would be substantially more wealthy than me before dating, I wouldn't care, like.. That's his money, right?

But I would understand that maybe living a certain life standard can be expected after marriage.. You could have some allowance written down to uphold a certain living situation or something...

Like if you have kids and you end up getting a divorce, it might not be fair for the kid and would also severely conflict a kid if there is a very substantial difference in life situation..