A decimal number is a number expressed in base 10, with the use of a decimal point to separate the integer and fractional parts. The antonyms of decimal number are Roman numeral, binary number, hexadecimal number, and octal number. A Roman numeral is a system of numeric notation using the letters I, V, X, L, C, D, and M. Binary numbers are a system of numeric notation based on 2 digits 0 and 1. Hexadecimal numbers are a system of numeric notation based on 16 digits, 0-9 and A-F. Octal numbers are a system of numeric notation based on 8 digits, 0-7. These systems are commonly used in computer science, mathematics, and engineering.