bi·na·ry / ˈbīˌnerē; -nərē/ • adj. 1. relating to, using, or expressed in a system of numerical notation that has 2 rather than 10 as a base. ∎ in binary format: it is stored as a binary file.2. relating to, composed of, or involving two things: testing the so-called binary, or dual-chemical, weapons.• n. (pl. -ries) 1. the binary system: binary notation: the device is counting in binary.2. something having two parts. ∎ a binary star.