The technical definition (the one that coders of the systems use) for debit card versus credit card is that debit cards are verified against a bite list at the time of transaction. read more
To reduce the normal credit balance in the bank's liability account, a debit entry is required. The name debit card also helps to distinguish it from a credit card. The use of a credit card means that the bank (or other financial institution) is making a loan or providing credit to the cardholder. read more
When you use a credit card, the bank is extending credit to you. The bank is paying for the transaction out of its cash, i.e. reducing its cash with a credit entry, and giving you a loan. You have 30 days to repay the bank. Notice that the terms are used from the bank's point of view. read more