Source : Webster's Revised Unabridged Dictionary (1913)

Middle \Mid"dle\, a. [OE. middel, AS. middel; akin to D. middel,
   OHG. muttil, G. mittel. ????. See {Mid}, a.]
   1. Equally distant from the extreme either of a number of
      things or of one thing; mean; medial; as, the middle house
      in a row; a middle rank or station in life; flowers of
      middle summer; men of middle age.

   2. Intermediate; intervening.

            Will, seeking good, finds many middle ends. --Sir J.
                                                  Davies.

   Note: Middle is sometimes used in the formation of
         selfexplaining compounds; as, middle-sized,
         middle-witted.

   {Middle Ages}, the period of time intervening between the
      decline of the Roman Empire and the revival of letters.
      Hallam regards it as beginning with the sixth and ending
      with the fifteenth century.

   {Middle class}, in England, people who have an intermediate
      position between the aristocracy and the artisan class. It
      includes professional men, bankers, merchants, and small
      landed proprietors

            The middle-class electorate of Great Britain. --M.
                                                  Arnold.

   {Middle distance}. (Paint.) See {Middle-ground}.

   {Middle English}. See {English}, n., 2.

   {Middle Kingdom}, China.

   {Middle oil} (Chem.), that part of the distillate obtained
      from coal tar which passes over between 170[deg] and
      230[deg] Centigrade; -- distinguished from the light, and
      the heavy or dead, oil.

   {Middle passage}, in the slave trade, that part of the
      Atlantic Ocean between Africa and the West Indies.

   {Middle post}. (Arch.) Same as {King-post}.

   {Middle States}, New York, New Jersey, Pennsylvania, and
      Delaware; which, at the time of the formation of the
      Union, occupied a middle position between the Eastern
      States (or New England) and the Southern States. [U.S.]

   {Middle term} (Logic), that term of a syllogism with which
      the two extremes are separately compared, and by means of
      which they are brought together in the conclusion.
      --Brande.

   {Middle tint} (Paint.), a subdued or neutral tint.
      --Fairholt.

   {Middle voice}. (Gram.) See under {Voice}.

   {Middle watch}, the period from midnight to four A. M.; also,
      the men on watch during that time. --Ham. Nav. Encyc.

   {Middle weight}, a pugilist, boxer, or wrestler classed as of
      medium weight, i. e., over 140 and not over 160 lbs., in
      distinction from those classed as {light weights}, {heavy
      weights}, etc.



   3. (Racing) A space marked out in the last part of a race
      course.

            The horse that ran the whole field out of distance.
                                                  --L'Estrange.

   Note: In trotting matches under the rules of the American
         Association, the distance varies with the conditions of
         the race, being 80 yards in races of mile heats, best
         two in three, and 150 yards in races of two-mile heats.
         At that distance from the winning post is placed the
         distance post. If any horse has not reached this
         distance post before the first horse in that heat has
         reached the winning post, such horse is distanced, and
         disqualified for running again during that race.

   4. (Mil.) Relative space, between troops in ranks, measured
      from front to rear; -- contrasted with {interval}, which
      is measured from right to left. ``Distance between
      companies in close column is twelve yards.'' --Farrow.

   5. Space between two antagonists in fencing. --Shak.

   6. (Painting) The part of a picture which contains the
      representation of those objects which are the farthest
      away, esp. in a landscape.

   Note: In a picture, the

   {Middle distance} is the central portion between the
      foreground and the distance or the extreme distance. In a
      perspective drawing, the

   {Point of distance} is the point where the visual rays meet.

   7. Ideal disjunction; discrepancy; contrariety. --Locke.

   8. Length or interval of time; period, past or future,
      between two eras or events.

            Ten years' distance between one and the other.
                                                  --Prior.

            The writings of Euclid at the distance of two
            thousand years.                       --Playfair.

   9. The remoteness or reserve which respect requires; hence,
      respect; ceremoniousness.

            I hope your modesty Will know what distance to the
            crown is due.                         --Dryden.

            'T is by respect and distance that authority is
            upheld.                               --Atterbury.

   10. A withholding of intimacy; alienation; coldness;
       disagreement; variance; restraint; reserve.

             Setting them [factions] at distance, or at least
             distrust amongst themselves.         --Bacon.

             On the part of Heaven, Now alienated, distance and
             distaste.                            --Milton.

   11. Remoteness in succession or relation; as, the distance
       between a descendant and his ancestor.

   12. (Mus.) The interval between two notes; as, the distance
       of a fourth or seventh.

   {Angular distance}, the distance made at the eye by lines
      drawn from the eye to two objects.

   {Lunar distance}. See under {Lunar}.

   {North polar distance} (Astron.), the distance on the heavens
      of a heavenly body from the north pole. It is the
      complement of the declination.

   {Zenith distance} (Astron.), the arc on the heavens from a
      heavenly body to the zenith of the observer. It is the
      complement of the altitude.

   {To keep one's distance}, to stand aloof; to refrain from
      familiarity.

            If a man makes keep my distance, the comfort is he
            keeps his at the same time.           --Swift.

Source : WordNet®

middle distance
     n : the part of a scene between the foreground and the
         background