The learned linkage of a stimulus-response pair - as typified by Pavlov's infamous dogs.

In the case of Pavlov's dogs, the dogs were repeatedly handed some juicy steak shortly after hearing the sound of a bell. After a while they came to associate the sound of the bell with the steak. When they heard the bell they immediately began to salivate in anticipation of the steak. They were conditioned to associate bell with steak.

-- JustMab