An agent is something that acts in an environment. An agent can, for example, be a person, a robot, a dog, a worm, a lamp, a computer program that buys and sells, or a corporation.

Agents interact with the environment with a body. An embodied agent has a physical body. A robot is an artificial purposive embodied agent. Sometimes agents that act only in an information space are called robots or bots, but we just refer to those as agents.

Agents receive information through their sensors. An agent’s actions depend on the information it receives from its sensors. These sensors may, or may not, reflect what is true in the world. Sensors can be noisy, unreliable, or broken, and even when sensors are reliable there still may be ambiguity about the world given the sensor readings. An agent must act on the information it has available. Often this information is very weak, for example, “sensor $s$ appears to be producing value $v$.”

Agents act in the world through their actuators, also called effectors. Actuators can also be noisy, unreliable, slow, or broken. What an agent controls is the message (command) it sends to its actuators. Agents often carry out actions to find more information about the world, such as opening a cupboard door to find out what is in the cupboard or giving students a test to determine their knowledge.