Source : Webster's Revised Unabridged Dictionary (1913)

Abstraction \Ab*strac"tion\, n. [Cf. F. abstraction. See
   {Abstract}, a.]
   1. The act of abstracting, separating, or withdrawing, or the
      state of being withdrawn; withdrawal.

            A wrongful abstraction of wealth from certain
            members of the community.             --J. S. Mill.

   2. (Metaph.) The act process of leaving out of consideration
      one or more properties of a complex object so as to attend
      to others; analysis. Thus, when the mind considers the
      form of a tree by itself, or the color of the leaves as
      separate from their size or figure, the act is called
      abstraction. So, also, when it considers whiteness,
      softness, virtue, existence, as separate from any
      particular objects.

   Note: Abstraction is necessary to classification, by which
         things are arranged in genera and species. We separate
         in idea the qualities of certain objects, which are of
         the same kind, from others which are different, in
         each, and arrange the objects having the same
         properties in a class, or collected body.

               Abstraction is no positive act: it is simply the
               negative of attention.             --Sir W.
                                                  Hamilton.

   3. An idea or notion of an abstract, or theoretical nature;
      as, to fight for mere abstractions.

   4. A separation from worldly objects; a recluse life; as, a
      hermit's abstraction.

   5. Absence or absorption of mind; inattention to present
      objects.

   6. The taking surreptitiously for one's own use part of the
      property of another; purloining. [Modern]

   7. (Chem.) A separation of volatile parts by the act of
      distillation. --Nicholson.

Source : WordNet®

abstraction
     n 1: a concept or idea not associated with any specific instance;
          "he loved her only in the abstract--not in person" [syn:
           {abstract}]
     2: the act of withdrawing or removing something
     3: the process of formulating general concepts by abstracting
        common properties of instances [syn: {generalization}, {generalisation}]
     4: an abstract painting
     5: preoccupation with something to the exclusion of all else
        [syn: {abstractedness}]
     6: a general concept formed by extracting common features from
        specific examples

Source : Free On-Line Dictionary of Computing

abstraction
     
        1. Generalisation; ignoring or hiding details to capture some
        kind of commonality between different instances.  Examples are
        {abstract data types} (the representation details are hidden),
        {abstract syntax} (the details of the {concrete syntax} are
        ignored), {abstract interpretation} (details are ignored to
        analyse specific properties).
     
        2.  Parameterisation, making something a function
        of something else.  Examples are {lambda abstractions} (making
        a term into a function of some variable), {higher-order
        function}s (parameters are functions), {bracket abstraction}
        (making a term into a function of a variable).
     
        Opposite of {concretisation}.
     
        (1998-06-04)