An agent is anything that can perceive its environment through sensors and acts upon that environment through effectors.

A human agent has sensory organs such as eyes, ears, nose, tongue and skin parallel to the sensors, and other organs such as hands, legs, mouth, for effectors.

A robotic agent replaces cameras and infrared range finders for the sensors, and various motors and actuators for effectors.

A software agent has encoded bit strings as its programs and actions.

Agent function is the description of what all functionalities the agent is supposed to do that in function provides mapping between perfect fitness is to the desired actions