Classical Conditioning: A learning process that occurs when two stimuli are repeatedly paired; a response that is at first elicited by the second stimulus is eventually elicited by the first stimulus alone. Taste aversion is an example of classical conditioning.
Conditioned Response: In classical conditioning, it's the learned response to the previously neutral stimulus. In taste aversion, this would be feeling nauseous at the sight or smell of a certain food.
Unconditioned Stimulus: This refers to something that triggers a natural response without any learning needed. For instance, in taste aversion, getting sick (the unconditioned stimulus) naturally leads to feeling nauseous (unconditioned response).