Definition of a robot?:

"A robot is an autonomous system which exists in the physical world, can sense its environment, and can act on it to achieve some goals."

Matarić, M. J. (2007) The Robotics Primer. Cambridge, Massachussetts: The MIT Press 

What components make up a typical robot?

A robot requires physical, real world, tangible components in order to be classified as a robot and have an effect or perform work on it's environment. By work I mean that the robot is able to perform an action using some type of force. Some examples of actions are manipulation of objects and locomotion. The components that make up a robot are:

1. Actuators (such as DC motors, servo motors and any other type of device that allows the robot to work)
2. Effectors (such as wheels, grippers, tracks etc. that are controlled by actuators to allow the robot to work)
3. Sensors (these components are the robotic equivalent to human sensory components. They allow the robot to see, hear, feel, smell etc. Some examples are photoresistors (detect light), bump switches (detect other physical objects), ultrasonic detectors (sense distance) and gyroscopes (detect orientation))
4. Controllers (this device uses the various sensor inputs/outputs to allow the robot to make decisions and perform actions).
5. And lastly a robot needs a physical body in order to mount and contain all the other previously mentioned components.