The Free On-line Dictionary of Computing (30 December 2018):

beam search

    An optimisation of the best first search graph
   search algorithm where only a predetermined number of paths
   are kept as candidates.  The number of paths is the "width of
   the beam".  If more paths than this are generated, the worst
   paths are discarded.  This reduces the space requirements of
   best first search.

   (2007-11-03)