A problem in Graph Theory requiring the most efficient (i.e., least total distance) Tour (i.e., closed path) a salesman can take through each of cities. No general method of solution is known, and the problem is NP-Hard.
See also Traveling Salesman Constants
References
Platzman, L. K. and Bartholdi, J. J. ``Spacefilling Curves and the Planar Travelling Salesman Problem.''
J. Assoc. Comput. Mach. 46, 719-737, 1989.