A credit card refers to a bank card that has a certain credit limit and can be paid first and then repaid within the credit limit. The card not only has functions such as deposits and withdrawals, transfers and consumption, but also allows you to enjoy various forms of points, discounts, promotions and other activities. The secondary credit card is attached to the primary credit card. The primary and secondary cards have the same functions and use the same account (that is, consumption with the secondary card will be included in the main card bill), but the card numbers are different. The supplementary cardholder must be the child, spouse or parent of the primary cardholder.