APA Dictionary of Psychology

a type of learning in which the organism successively tries various responses in a situation, seemingly at random, until one is successful in achieving the goal. Across successive trials, the successful response is strengthened and appears earlier and earlier. Maze learning, with its eventual elimination of blind-alley entrances, is an example of trial-and-error learning. The term derives from the stimulus–response theory of Edward L. Thorndike as an explanation of instrumental or reinforcement learning, although Thorndike initially preferred the more descriptive phrase trial-and-accidental success.