CR, or Conditioned Reflex - A learned response to a specific conditioned stimulus through association (temporal pairing) with some other stimulus that already produces the desired response.

In classical conditioning experiments, such as those performed by Pavlov, the "other" stimulus is often an unconditioned stimulus (US), which is a stimulus that produces an innate response (an unconditioned response, or UR). That is, a response that the animal exhibits from birth.

Learned responses are learned behaviors. Many learned behaviors may ultimately be traceable to conditioned associations with unconditioned stimuli.