Okay, so pacta sunt servanda is a Latin phrase that means promises must be kept. It means that when we make a promise or an agreement with someone, we must keep our end of the bargain.
Remember how mommy and daddy promised you that they would take you to the park on Saturday? That's a promise, and they need to keep it because they made it to you.
Just like how we make promises and have agreements with people, countries and governments also make promises and agreements with each other. And they need to keep those promises too, just like we do.
So remember, pacta sunt servanda means keeping your promises, even if it's hard, because it's the right thing to do.