is generally defined as the science of behavior and mental processes and the application of the resulting findings to the solution of problems.
The word thus simultaneously refers to a science (involving the study of the behavior of humans and animals) and to various interventions (treatments and therapies) in the mental processes and behavioral patterns of people. It is a branch of science that studies the cognitive, perceptual, and behavioural characteristics of human beings. The "how and why" of our behavior.
"To cause an organism to respond in a specific manner to a conditioned stimulus in the absence of an unconditioned stimulus."