A damage waiver is like an agreement you make with the person who is letting you borrow something valuable. The agreement says that you won't have to pay them a lot of money if you accidentally damage their thing while you are using it.
For example, imagine you want to borrow your friend's bike. If your friend asks you to sign a damage waiver, they are saying that you won't have to pay for the bike if you accidentally break it.
It's kind of like a promise to be extra careful when using someone else's things, but also a promise to not worry too much if something does happen. Of course, this doesn't mean you can be reckless with other people's things or purposefully damage them!
A damage waiver is often used when people rent or lease things, like cars or vacation homes. It's important to read these agreements carefully and understand what you're responsible for, so you can avoid any unexpected costs.