Chargeback
A chargeback is when a customer asks their bank to take the money back from you, instead of asking you.
In a simple example
A customer says: I did not buy this. The bank pulls the money from your account and asks you to prove the sale.
Why it matters to you
It costs you the money plus a fee, and too many can make your payment service close your account.
Do not confuse with
A refund is a choice you make. A chargeback is a decision of the bank.