A debit card (also known as a bank card) is a plastic card which provides an alternative payment method to cash when making purchases. Functionally, we can say it an electronic check, as the funds are withdrawn directly from one bank account to other or from the remaining balance on the card. In some cases, the cards are designed exclusively for Internet, so there is no physical card.
The use of debit cards has become very popular in many countries and has overtaken the usage of a cheque. Like credit cards, debit cards are used widely for any kind of purchase over telephone or Internet.
Debit cards allow instant withdrawal of cash, like ATM cards and like a cheque guarantee card. Merchants can offer "cashback"/"cashout" facilities to customers,where a customer can withdraw cash along with their purchase.
Difference :
For consumers, the difference between a "debit card" and a "credit card" is that the debit card deducts the balance from a deposit account, like a checking account, whereas the credit card allows the consumer to spend money on credit to the issuing bank. In other words, a debit card uses the money you have and a credit card uses the money you don't.
