Heuristic Search Hypothesis: The solutions to problems are represented as symbol structures. A physical symbols system exercises its intelligence in problem solving by search—that is, by generating and progressively modifying symbol structures until it produces a solution structure.
Newell & Simon (1976, p.120)
Heuristic Search: A search that uses special knowledge about a problem domain to find solutions more efficiently. For example, a search of possible moves in a chess game could be aided by a set of heuristics that tell the computer to avoid useless lines of attack, to maintain center control, and so forth.