What is stimulus?

A stimulus is any object or event that elicits a response from an organism. It can be anything that triggers a reaction or change in behavior, such as a sound, smell, touch, or visual cue. Stimuli can be internal or external, and they can be positive (rewarding) or negative (aversive). In psychology and neuroscience, stimuli are often used in experiments to study how organisms respond to different environmental cues.