A stimuli is anything that can trigger a physical or behavioral change.
The changes in the environment to which living things respond are called stimuli. The living things show response to external stimuli such as heat, light , touch, sound, smell, taste, water and chemicals.
It can be internal or external both.
When diverse organs works collectively in a scientific way to supply a reaction to the stimulus, this is known as coordination.
Stimuli is essentially anything that triggers a receptor for one of those senses.
You can understand this with an example that would be the receptors on our skin which sense a stimulus like pain. Sense organs contain groups of receptors that respond to specific stimuli.
