Classical Conditioning is the term normally used to describe the associative learning process first explored by Pavlov in his experiments with dogs.

Classical conditioning describes the ability of an animal to learn (be "conditioned") to associate a new stimulus for which it has no inherent response, with a stimulus to which it responds inherently.

The stimulus that the animal must learn to respond to is called the conditioned stimulus and its learned response to it is called a conditioned response.

The stimulus the animal inherently knows how to respond to is called the unconditioned stimulus, and its inherently known response to it is called an unconditioned response

	Unconditioned (inherent behavior)	Conditioned (learned behavior)
S t i m u l u s	US An Unconditioned Stimulus is a stimulus which evokes a hard-wired, inherent response from the animal. In other words, the animal did not have to learn the behavior, and responds to US based on knowledge it has at birth.	CS A Conditioned Stimulus is a stimulus for which there is no hard-wired, inherent response. This describes behavior that the animal is not born with and must learn. In other words, the animal must be conditioned to respond to CS.
R e s p o n s e	UR An Unconditioned Response is a response to stimulus that is hard-wired in the animal from birth. Unconditioned Responses do not need to be learned (the animal does not need to be conditioned to produce the response).	CR A Conditioned Response is one that must be taught to the animal. In other words, the animal must be conditioned to produce the response.