The Collaborative International Dictionary of English v.0.48:

Congestion \Con*ges"tion\ (?; 106), n. [L. congestio: cf. F.
   congestion.]
   1. The act of gathering into a heap or mass; accumulation.
      [Obs.]
      [1913 Webster]

            The congestion of dead bodies one upon another.
                                                  --Evelyn.
      [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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

The Free On-line Dictionary of Computing (19 January 2023):

congestion

    The condition that arises when the amount of
   data that senders want to send down a communication channel
   exceeds its capacity.  Typically this will result in some
   packets being delayed, thus increasing the average latency.

   (2014-05-04)