Source : Webster's Revised Unabridged Dictionary (1913)

Binary \Bi"na*ry\, a. [L. binarius, fr. bini two by two, two at
   a time, fr. root of bis twice; akin to E. two: cf. F.
   binaire.]
   Compounded or consisting of two things or parts;
   characterized by two (things).

   {Binary arithmetic}, that in which numbers are expressed
      according to the binary scale, or in which two figures
      only, 0 and 1, are used, in lieu of ten; the cipher
      multiplying everything by two, as in common arithmetic by
      ten. Thus, 1 is one; 10 is two; 11 is three; 100 is four,
      etc. --Davies & Peck.

   {Binary compound} (Chem.), a compound of two elements, or of
      an element and a compound performing the function of an
      element, or of two compounds performing the function of
      elements.

   {Binary logarithms}, a system of logarithms devised by Euler
      for facilitating musical calculations, in which 1 is the
      logarithm of 2, instead of 10, as in the common
      logarithms, and the modulus 1.442695 instead of .43429448.
      

   {Binary measure} (Mus.), measure divisible by two or four;
      common time.

   {Binary nomenclature} (Nat. Hist.), nomenclature in which the
      names designate both genus and species.

   {Binary scale} (Arith.), a uniform scale of notation whose
      ratio is two.

   {Binary star} (Astron.), a double star whose members have a
      revolution round their common center of gravity.

   {Binary theory} (Chem.), the theory that all chemical
      compounds consist of two constituents of opposite and
      unlike qualities.

Binary \Bi"na*ry\, n.
   That which is constituted of two figures, things, or parts;
   two; duality. --Fotherby.

Source : WordNet®

binary
     adj 1: of or pertaining to a number system have 2 as its base; "a
            binary digit"
     2: consisting of two (units or components or elements or terms)
        or based on two; "a binary star is a system in which two
        stars revolve around each other"; "a binary compound";
        "the binary number system has two as its base"

binary
     n : a system of two stars that revolve around each other under
         their mutual gravitation [syn: {binary star}, {double
         star}]

Source : Free On-Line Dictionary of Computing

binary
     
        1.  {Base} two.  A number representation
        consisting of zeros and ones used by practically all computers
        because of its ease of implementation using digital
        electronics and {Boolean algebra}.
     
        2.  Any file format for {digital} {data} encoded
        as a sequence of {bit}s but not consisting of a sequence of
        printable {characters} ({text}).  The term is often used for
        executable {machine code}.
     
        Of course all digital data, including characters, is actually
        binary data (unless it uses some (rare) system with more than
        two discrete levels) but the distinction between binary and
        text is well established.
     
        3.  A description of an {operator} which takes
        two {arguments}.  See also {unary}, {ternary}.
     
        (1998-07-29)