1. The representation of symbols in a source alphabet by strings of binary digits, i.e. a binary code. The most commonly occurring source alphabet consists of the set of alphanumeric characters. See code.
2. The encoding of a number into a binary string in which the ith bit from the end carries weight 2i. For example, 13 is represented by 1101. This encoding of natural numbers can be extended to cover signed integers and fractions. See also fixed-point notation, floating-point notation, radix complement.
3. (of a set A) Any assignment of distinctive bit strings to the elements of A. See also character encoding, Huffman encoding.