Two-out-of-five code

In telecommunication, a two-out-of-five code is a binary-coded decimal notation in which (a) each decimal digit is represented by a binary numeral consisting of five binary digits of which two are of one kind, called "ones," and three are of the other kind, called "zeros" and (b) the usual weights assigned to the digit positions are 0-1-2-3-6, except that "zero" is represented as 01100.

Source: From Federal Standard 1037C