Okay kiddo, let me explain pledge in laws. Imagine you have a toy that you really love and you want to let your friend play with it. But you don't want your friend to lose it or break it. So, you ask your friend to promise that they will take good care of your toy while they are playing with it. That promise your friend made is similar to a pledge in laws.
In the same way, some people give something valuable as security when they borrow money from a bank or a lender. This valuable thing is called a pledge. It is like when you ask your friend to promise to take care of your toy in exchange for playing with it. The borrower promises to return the money they borrowed and if they don't, then the bank or lender has the right to take the pledged item and sell it to get their money back.
So, a pledge is a promise or agreement made by a borrower to return what they have borrowed or give something valuable as security for what they have borrowed.