Think about your piggy bank with lock and key. Only you can take money out from it when you need, since you have the key to open the lock. Right ?
Have you seen your parents taking out money from a machine sometimes when you go shopping? They call it ATM. But How do they do it without lock and key?
Lets understand how.
Piggy Bank with lock = ATM (Any Time Money)
Key = Plastic card
An ATM is a piggy bank with lock. The way to unlock the ATM for taking out money is not a key like yours , but a plastic card. When this card is swiped on the machine, it asks for a personal code (PIN),a password only your parent knows. The machine then identifies your parent and allows them to withdraw as much money as they need.
There is only one difference, The ATM is one big piggy bank that many grown ups share.