Source : Free On-Line Dictionary of Computing

best effort
     
         A classification of low priority network traffic,
        used especially the {Internet}.
     
        Different kinds of traffic have different priorities.
        {Videoconferencing} and other types of {real-time}
        communication, for example, require a certain minimum
        guaranteed {bandwidth} and {latency} and so must be given a
        high priority.  {Electronic mail}, on the other hand, can
        tolerate an arbitrarily long delay and is classified as a
        "best-effort" service.
     
        [Scientific American, Nov. 1994, pp. 83-84].
     
        (1995-04-04)