See binary in Webster's New World College Dictionary
adjective
made up of two parts or things; twofold; double
designating or of a number system in which the base used is two, each number being expressed in powers of two by using only two digits, specif. 0 and 1
designating or of a musical form consisting of two closely related sections
Chem. composed of two elements or radicals, or of one element and one radical: binary compounds