A debit card is tied to a bank account, when you spend money it comes from that account.
A prepaid card is tied only to the money you put down when you paid for the card. The bank that backs it creates a temporary account with only that amount in it.
The biggest difference is that the debit card will have personal information tied to it. Your name, bank account, etc. A prepaid card is anonymous, especially if you paid cash for it.
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