binary number system A method of representing numbers that has 2 as its base and uses only the digits 0 and 1. Each successive digit represents a power of 2. For example, 10011 represents (1 × 2^{4}) + (0 × 2^{3}) + (0 × 2^{2}) + (1 × 2^{1}) + (1 × 2^{0}), or 16 + 0 + 0 + 2 + 1, or 19.
in mathematics, positional numeral system employing 2 as the base and so requiring only two different symbols for its digits, 0 and 1, instead of the usual 10 different symbols needed in the decimal system. The importance of the binary system to information theory and computer technology derives mainly from the compact and reliable manner in which 0s and 1s can be represented in electromechanical devices with two states-such as "on-off," "open-closed," or "go-no go." See numerals and numeral systems.