Classical conditioning is a type of learning where an originally neutral stimulus becomes associated with an emotional or physiological response after being repeatedly paired with an unconditioned stimulus that elicits a natural response. Key terms in classical conditioning include the unconditioned stimulus, which automatically elicits an unconditioned response, and the conditioned stimulus, which was originally neutral but after conditioning can elicit a conditioned response similar to the unconditioned response due to its association with the unconditioned stimulus through repeated pairing. Classical conditioning involves simple association formation and learning processes.