The base of a binary number is 2. Binary is a base-2 numeral system, which means it uses only two digits: 0 and 1. Each digit in a binary number is referred to as a "bit" (short for binary digit). In contrast, the decimal system (base-10) uses ten digits (0 through 9), and the hexadecimal system (base-16) uses sixteen digits (0-9 and A-F, where A stands for 10, B for 11, and so on). Binary is commonly used in computing and digital electronics to represent information using combinations of 0s and 1s.