The term "stimulus" (plural: stimuli) has several related meanings:

• In physiology, a stimulus is something external that elicits or influences a physiological or psychological activity or response.
• In psychology, anything effectively impinging upon any of the sensory apparatuses of a living organism, including physical phenomena both internal and external to the body.
• In other fields, a stimulus is anything that may have an impact on a system; for example, an economic stimulus.

In most contexts, a stimulus can be described as "stimulating," thereby causing "stimulation." Although related, the word's meaning is distinct from that of "stimulant."

See also

• Response
• Stimulus-response model.