A procedure used to provide solutions to decision problems but which are not guaranteed as best or optimal because they often depend on good judgment in the first place. Literally, leading toward discovery, finding out.
(Wideman Comparative Glossary of Common Project Management Terms v2.1)
Heuristic – A rule of thumb, simplification, or educated guess that reduces or limits the search for solutions in domains that are difficult and poorly understood. Unlike algorithms , heuristics do not guarantee optimal, or even feasible , solutions and are often used with no theoretical guarantee. (The Free On-line Dictionary of Computing )