Source : Webster's Revised Unabridged Dictionary (1913)

Congestion \Con*ges"tion\ (?; 106), n. [L. congestio: cf. F.
   congestion.]
   1. The act of gathering into a heap or mass; accumulation.
      [Obs.]

            The congestion of dead bodies one upon another.
                                                  --Evelyn.

   2. (Med.) Overfullness of the capillary and other blood
      vessels, etc., in any locality or organ (often producing
      other morbid symptoms); local hyper[ae]mia, active or
      passive; as, arterial congestion; venous congestion;
      congestion of the lungs.

Source : WordNet®

congestion
     n 1: excessive accumulation of blood or other fluid in a body
          part
     2: excessive crowding; "traffic congestion" [syn: {over-crowding}]

Source : Free On-Line Dictionary of Computing

congestion
     
        When the offered load of a data communication path exceeds the
        capacity.