When your bank account is debited, it means money is taken out of the account. The opposite of a debit is a credit, in which case money is added to your account. Typically, your account is debited when you use a debit card, which, as its name indicates, enables you to take money from your bank account and use it to purchase goods and services.
The first thing that happens when you use your debit card to make a purchase is your bank is notified of the purchase electronically. This happens automatically and, usually, instantaneously, when you swipe your card or enter it on a website to make an online purchase. Because a transaction generally takes 24 to 72 hours to complete, the bank puts a hold on your account for the amount of the transaction. This action prevents you from using the money for something else. Ideally, the hold lasts long enough to earmark the funds until the transaction is complete.
Next, the retailer from whom you made your purchase sends the details of the transaction to your bank. Your bank reviews the details and, assuming everything looks good, electronically transfers the purchase price to the retailer, effectively removing those funds from your account. In banking parlance, the bank debits the purchase price from your account.
Every financial transaction involves a debit and a credit. When you make a purchase using your debit card, for example, the purchase price is debited from your bank account, but it is also credited to the account of the retailer from whom you made the purchase.