Instant card number allows you to use your card before the issuer actually sends you one. It is the same number that you will see on the card itself, but the security code is typically only temporary and will be different on the physical card. You can use it for making purchases before you receive the physical card. If the issuer gives you information about your instant number, be sure to write it down immediately or take a screenshot. You will not be allowed to request the instant card number again and will have to wait for your card to arrive if you want to use it.