Classical conditioning - the animal learns to associate a previously neutral stimulus with a response. It can occur throughout life but only if certain conditions are met e.g. a short time gap between the neutral stimulus (e.g. bell) and the response (e.g. salivation).
This learning can be lost.
Classical Conditioning is a learned association between a meaningful stimulus (Unconditioned Stimulus) to a previously neutral stimulus (Conditioned Stimulus), causing the CS to elicit a similar response.
Unconditioned Stimulus (US) means any non-habituating stimulus that elicits a response without prior training.
Conditioned Stimulus (CS) means any stimulus that does not initially elicit a particular response (neutral) but will elicit the response because of pairing with the US.
Unconditioned Responses are a reflex or autonomic response (physiological or emotional) to a stimulus that occurs without the necessity of prior conditioning.
Conditioned Response is a response like unconditioned responses that comes to be made to the conditioned stimulus following classical conditioning.