Although Ivan Pavlov received a Nobel Prize for work on digestion, his most important work was in the study of classical conditioning with the famous Pavlov's Dog experiment.
This experiment involved conditioning a dog to salivate in response to an Neutral Stiumulus (a light, or bell for instance). When presenting the dog with food (Unconditioned Stimulus) it elicits an Unconditioned Response (salivation). By presenting the Neutral Stimulus and Unconditioned Stimulus in synchrony we may condition the dog to respond to the Neutral Stimulus; The dog makes the association that light and food go together and so will salivate in response to the light alone. The light has now become a Conditioned Stimulus, which ellicits the Conditioned Response (salivation).
The experiment is discussed further at: Classical conditioning
Pavlov's Dog is also the name of a Public house in Reading, Berkshire in the United Kingdom.
(As it happens, I will actually be going there a little later this afternoon!)
31 St. Marys Butts
Reading RG1 2LN