blank credit card; unregistered card
Refers to a credit card or similar card that has been issued but not yet activated or personalized with a card number, name, etc. Often used in contexts of card issuance or fraud prevention.
When I opened a new account, they first sent me a blank card.
You can't use it yet while it's still a blank card, so you need to register it online.
Compound of 生 (なま, 'raw, unprocessed') and カード ('card'), literally meaning a card in its raw, unactivated state.