Relating to, composed of, or involving two things. The binary system is fundamental to computer operations, using only two digits, 0 and 1.
Consisting of two parts or elements. The binary star system consists of two stars orbiting around a common center of mass.
Involving a choice or condition of two alternatives only. The decision was binary: either accept the offer or decline it.
Relating to or using a system of numerical notation that has 2 as its base. Computers operate on binary code, where each bit is either 0 or 1.