A **binary number** is a number expressed in the **base-2 numeral system** or **binary numeral system**, a method for representing numbers that uses only two symbols for the natural numbers: typically "0" (zero) and "1" (one). A *binary number* may also refer to a rational number that has a finite representation in the binary numeral system, that is, the quotient of an integer by a power of two.

The base-2 numeral system is a positional notation with a radix of 2. Each digit is referred to as a bit, or binary digit. Because of its straightforward implementation in digital electronic circuitry using logic gates, the binary system is used by almost all modern computers and computer-based devices, as a preferred system of use, over various other human techniques of communication, because of the simplicity of the language and the noise immunity in physical implementation.^{[1]}