A credit card number is a unique 16-digit number exclusive to every credit card. The first digit helps in identifying the credit card company. For example, VISA credit cards begin with the number "4", while MasterCard's start with the digit "5". Similarly, Discover credit cards start with the number "6". Second to sixth-placed digits help in identifying the bank. The 7th to 15th digits signify the cardholder's account number. The last remaining number is termed as the check digit. It is automatically generated based on the remaining numbers. The check digit helps in eliminating any errors.