What are the three numbers on the back of the credit card?

The three numbers on the back of the credit card are CVV2 verification codes.

According to official website's "I love my card" query, the three digits on the back of the credit card are the verification code of the credit card and also a security code, commonly known as the "last three codes". It is the verification code used for indirect credit card spending. For example, online payment transactions need this verification code, which generally refers to the last three digits of the seven-digit signature column on the back of the credit card.

It should be noted that this verification code does not refer to the password of the credit card. Once leaked, it is likely to lead to the theft of credit cards.