Card tokenization replaces the real card details with a random digital substitute (a token) that can be used safely for payments in a phone or on a website.
In plain words
When you add a card to Apple Pay or Google Pay, the payment system and the bank issue a token: a separate number tied to your device or to a merchant. The merchant and the terminal see the token and the real card number is not passed on, so a data leak at a merchant does less harm. A token can be revoked without reissuing the card itself.
Example. You lose a phone with Apple Pay: the bank can revoke that phone’s token without blocking the plastic card. Paying with the card on other devices keeps working.