What is an overdraft?
Overdrafts occur when you make a transaction using more funds than are currently available in your checking account. When you overdraw, whether it is through a debit card purchase or ATM withdrawal, the bank can either process or reject the transaction. If the bank chooses to pay the transaction (even though you don't have enough money in your account), you will be charged an "overdraft" fee.
For example, if you have just $1 in your account but you pay for a $2 coffee, the bank can decide to approve your transaction and charge an overdraft fee.