In mathematics and digital circuits, binary refers to the counting system with the base number of 2. The system represented by the base number of 2 is binary. In this system, it is usually represented by two different symbols 0 (for zero) and 1 (for one). In digital electronic circuit, the implementation of logic gate directly uses binary, so modern computer and computer dependent equipment use binary. Each number is called a bit.

Source: @bigbad_kenn