bi·na·ry 
(bīnə-rē)
(bīnə-rē)adj.
1. Characterized by or consisting of two parts or components; twofold.
2.
a. Of or relating to a system of numeration having 2 as its base.
b. Of or relating to a system of encoding data using only 0's and 1's.
3. Chemistry Consisting of or containing only two kinds of atoms.
4. Of or employing two comparatively nontoxic chemicals that combine to produce a deadly poison: binary weapons; a binary nerve agent.
5. Music Having two sections or subjects.
n. pl. bi·na·ries
1. A number system having 2 as its base.
2. A file that contains the executable version of a computer program.
3. A binary star.
[Middle English binarie, from Late Latin bīnārius, from Latin bīnī, two by two; see dwo- in the Appendix of Indo-European roots.]