Question

What is stimulus and response?

Answer 1

A stimulus is felt by an organism's senses which are sensitive parts of his physiology. ... When any part of an organism or of man's sensory organs is stimulated, a reaction or a responsewill result. A response is the behavior that is manifested by a living organism which is the result of an external or internal stimulus.

A stimulus is anything that causes you to react, for example, the smell of food and your mouth watering.
Responses are actions of the body: muscle contractions, gland secretions, or brain actions. Examples of responses include: muscle movements, like pressing a key with a finger; the product of muscle movements, like speaking; glands secreting, like salivation or perspiration or increased adrenalin flow inside the body; brain reactions, like changes in the EEG ("brain waves").