moore graph

from The Free On-line Dictionary of Computing (8 July 2008)

Moore graph

   A {graph} which achieves the {Moore bound}.  These are
   {complete graphs}, {polygon graphs} ({regular graphs} of
   {degree} 2) and three others: (nodes, degree, diameter) =
   (10,3,2), (50,7,2) and the possible but undiscovered
   (3250,57,2).