Source : Webster's Revised Unabridged Dictionary (1913)

Tailing \Tail"ing\, n. (Elec.)
   A prolongation of current in a telegraph line, due to
   capacity in the line and causing signals to run together.

Tailing \Tail"ing\, n.
   1. (Arch.) The part of a projecting stone or brick inserted
      in a wall. --Gwilt.

   2. (Surg.) Same as {Tail}, n., 8
      (a) .

   3. Sexual intercourse. [Obs.] --Chaucer.

   4. pl. The lighter parts of grain separated from the seed
      threshing and winnowing; chaff.

   5. pl. (Mining) The refuse part of stamped ore, thrown behind
      the tail of the buddle or washing apparatus. It is dressed
      over again to secure whatever metal may exist in it.
      Called also {tails}. --Pryce.

Source : WordNet®

tailing
     adj : following surreptitiously; keeping under surveillance;
           "always on guard against shadowing submarines" [syn: {shadowing}]
     n : the act of following someone secretly [syn: {shadowing}]