A code in which a string of binary digits represents a decimal digit. In the natural binary-coded decimal (NBCD) system, each decimal digit 0 through 9 is represented by the string of four bits whose binary numerical value is equivalent to the decimal digit. For example, 3 is represented by 0011 and 9 is represented by 1001. The NBCD code is the 8421-code such that the weighted sum of the bits in a codeword is equal to the coded decimal digit. See also EBCDIC, packed decimal.