Q. Define the Classical conditioning?

Pavlov's near the beginning work on dogs was known as classical conditioning. Pavlov exposed that when dogs were fed meat powder they salivated. Pavlov then exposed that if a bell were rung before the dogs were fed the dogs would begin salivating in anticipation of being fed (this was efficient because they could then begin digesting the meat powder immediately). Pavlov then found that subsequent to the meat had been paired with the meat powder sufficient times Pavlov could ring the bell without feeding the dogs and they would still salivate.

In the terminology of classical conditioning the meat powder was an unconditioned stimulus (US) and the salivation was when preceded by the meat powder an unconditioned response (UR). I.e. it is a biologically hard-wired response to salivate when you are fed. By pairing the bell among the unconditioned stimulus the bell became a conditioned stimulus (CS) and salivation in response to the bell (with no meat powder) became a conditioned response (CR).

Many modern day advertisers utilize classical conditioning in some way. Consider this series: