Sensory pre-conditioning is a behavioral concept and a type of higher order conditioning that involves associating two .
Two conditioned stimuli are paired together then one of them is paired with an unconditioned stimulus (US). This causes the other, non-paired conditioned stimulus to be able to elicit a response when it is paired with the US. For example, you condition an animal to associate a whistle and a bell together.
You then condition the animal to pair the bell with food which causes salivation. Sensory pre-conditioning occurs when the whistle causes salivation even though the animal wasn't specifically conditioned to have that response.