Classical conditioning is a type of learning where organisms learn to associate stimuli. Ivan Pavlov, a famous Russian physiologist, discovered classical conditioning through his dog experiments. He found that a dog could learn to associate a neutral stimulus, like a bell, with an unconditioned stimulus, like food, which elicits an unconditioned response, like salivation. After repeated pairings, the neutral stimulus alone could elicit the conditioned response of salivation. Pavlov's experiments demonstrated key concepts of classical conditioning like acquisition, extinction, spontaneous recovery, stimulus generalization, and discrimination. Classical conditioning principles can be applied to areas like teaching and advertising.