Refunding is when you give your money back to someone because they didn't get what they wanted or something went wrong.
Imagine if you went to the store with your mom to buy a toy. You picked out a cool toy car and your mom paid for it with her money. But then you got home and realized the toy car was broken and couldn't be played with.
If you took the toy car back to the store and showed them it was broken, they would give your mom her money back. This is called a refund.
And why do they do this? Because the store wants you and your mom to be happy with what you buy from them. So if something goes wrong, they will give you your money back to make things right.