What type of number is expressed using base 10?

A decimal number is expressed using base 10, which means it utilizes ten digits (0 through 9) to represent values. This is the standard numbering system used in daily life for counting, measurements, and calculations. In contrast, binary numbers are expressed using base 2 (using only the digits 0 and 1), octal numbers use base 8 (digits 0 to 7), and hexadecimal numbers use base 16 (digits 0 to 9 and letters A to F). Therefore, the decimal number system is uniquely related to base 10, making it the correct answer.