**1.** Any notation that uses two different characters, usually the digits 0 and 1.

*Note:* Data encoded in binary notation need not be in the form of a pure binary numeration system; *e.g.,* they may be represented by a Gray code.

**2.** A scheme for representing numbers, which scheme is characterized by the arrangements of digits in sequence, with the understanding that successive digits are interpreted as coefficients of successive powers of base 2.

Source: from Federal Standard 1037C and from MIL-STD-188