On the most basic level, human beings are made up of five major components:

A body structure
A muscle system moves the body structure
A sensory system that receives information about the body and the surrounding environment
A power source to activate the muscles and sensors
A brain system that processes sensory information and tells the muscles what to do

Of course, we also have some intangible attributes, such as intelligence and morality, but on the sheer physical level, the list above about covers it.

A robot is made up of the very same components. A basic typical robot has a movable physical structure, a motor of some sort, a sensor system, a power supply and a computer "brain" that controls all of these elements. Essentially, robots are human-made versions of animal life — they are machines that replicate human and animal behaviour.

Joseph Engelberger, a pioneer in industrial robotics, once remarked, "I don't know how to define one, but I know one when I see one!" If you consider all the different machines people call robots, you can see that it's nearly impossible to come up with a comprehensive definition. Everybody has a different idea of what constitutes a robot.

You've probably heard of several of these famous robots:

R2-D2 and C-3PO: The intelligent, speaking robots with loads of personality in the "Star Wars" movies
Sony's AIBO: A robotic dog that learns through human interaction
Honda's ASIMO: A robot that can walk on two legs like a person
Industrial robots: Automated machines that work on assembly lines
Lieutenant Commander Data: The almost-human android from "Star Trek"
BattleBots: The remote-control fighters from the long-running TV show
Bomb-defusing robots
NASA's Mars rovers
HAL: The ship's computer in Stanley Kubrick's "2001: A Space Odyssey"
Roomba: The vacuuming robot from iRobot
The Robot in the television series "Lost in Space"
MINDSTORMS: LEGO's popular robotics kit

All of these things are considered robots, at least by some people. But you could say that most people define a robot as anything that they recognize as a robot. Most roboticists (people who build robots) use a more precise definition. They specify that robots have a reprogrammable brain (a computer) that moves a body.

How Robots Work

In the next section, we'll look at the major elements found in most robots today.

R2-D2 (left) and C-3PO attend the premiere of "Star Wars: The Force Awakens" in 2015 in Hollywood, California. For many people, these two figures represent what robots look like. FRAZER HARRISON/GETTY IMAGES

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