(2) In Binary number system, 111 represents seven. In mathematics and digital electronics, a binary number is a number that is expressed in the base-2 numeral system or binary numeral system, which uses only two symbols: typically 0 (zero) and 1 (one). The base-2 numeral system is a positional notation with a radix of 2. Each digit is referred to as a bit. Other number systems include octal, decimal, hexadecimal etc.