An agent is anything that can be viewed as perceiving its environment through sensors and SENSOR acting upon that environment through actuators. This simple idea is illustrated in Figure.
A human agent has eyes, ears, and other organs for sensors and hands, legs, mouth, and other body parts for actuators.
A robotic agent might have cameras and infrared range finders for sensors and various motors for actuators.
A software agent receives keystrokes, file contents, and network packets as sensory inputs and acts on the environment by displaying on the screen, writing files, and sending network packets.