Stimulus

A stimulus is the following:

In physiology, a stimulus (physiology) is something external that elicits or influences a physiological or psychological activity or response.
In psychology, anything effectively inpinging upon any of the sensory apparatuses of a living organism, including physical phenomena both internal and external to the body.
In general, a stimulus may affect other things than living creatures; for example, one speaks also of economic stimulus, or stimulating a discussion.

See also