Heuristics: Science of guessing; from heuristic: method of producing useful guesses about something. (In Dutch there is next to Simon Stevin's Dutch term for mathematics "wiskunde" the nice term "giskunde" for heuristics).
One useful general characterization of heuristic, that precisifies the above a little, is: A heuristic is a method, way of acting, principle(s) of choosing, that helps one find useful or interesting conclusions. The criterion is not deductive validity or truth or probability, but the help provided with finding conclusions of a certain kind or with solving problems of a certain kind.

See also: Analogy
Literature:
Bernouilli, Bono, Gardner, Ghiselin, Groner etc., Hadamard, Hawkins, Koestler, Polya,
