Defining characteristics

KITT is mentally anthropomorphic, while ASIMO is physically anthropomorphic

While there is no single correct definition of "robot", a typical robot will have several or possibly all of the following properties.

• It is composed entirely, or almost entirely, from artificial substances.
• It can sense its environment, and manipulate or interact with things in it.
• It has some ability to make choices based on the environment, often using automatic control or a preprogrammed sequence.
• It is programmable.
• It moves with one or more axes of rotation or translation.
• It makes dexterous coordinated movements.
• It moves without direct human intervention.
• It appears to have intent or agency.

The last property, the appearance of agency, is important when people are considering whether to call a machine a robot, or just a machine. (See anthropomorphism for examples of ascribing intent to inanimate objects.)

Mental agency
For robotic engineers, the physical appearance of a machine is less important than the way its actions are controlled. The more the control system seems to have agency of its own, the more likely the machine is to be called a robot. An important feature of agency is the ability to make choices.

• A clockwork car is never considered a robot.
• A remotely operated vehicle is sometimes considered a robot (or telerobot).
• A car with an onboard computer, like Bigtrak, which could drive in a programmable sequence, might be called a robot.
• A self-controlled car which could sense its environment and make driving decisions based on this information, such as the 1990s driverless cars of Ernst Dickmanns or the entries in the DARPA Grand Challenge, would quite likely be called a robot.
• A sentient car, like the fictional KITT, which can make decisions, navigate freely and converse fluently with a human, is usually considered a robot.

Physical agency
However, for many laymen, if a machine appears to be able to control its arms or limbs, and especially if it appears anthropomorphic or zoomorphic (e.g. ASIMO or Aibo), it would be called a robot.

• A player piano is rarely characterized as a robot.
• A CNC milling machine is very occasionally characterized as a robot.
• A factory automation arm is almost always characterized as an industrial robot.
• An autonomous wheeled or tracked device, such as a self-guided rover or self-guided vehicle, is almost always characterized as a mobile robot or service robot.
• A zoomorphic mechanical toy, like Roboraptor, is usually characterized as a robot.
• A mechanical humanoid, like ASIMO, is almost always characterized as a robot, usually as a service robot.

Even for a 3-axis CNC milling machine using the same control system as a robot arm, it is the arm which is almost always called a robot, while the CNC machine is usually just a machine. Having eyes can also make a difference in whether a machine is called a robot, since humans instinctively connect eyes with sentience. However, simply being anthropomorphic is not a sufficient criterion for something to be called a robot. A robot must do something; an inanimate object shaped like ASIMO would not be considered a robot.

Definitions

A laparoscopic robotic surgery machine

It is difficult to compare numbers of robots in different countries, since there are different definitions of what a "robot" is. The International Organization for Standardization gives a definition of robot in ISO 8373: "an automatically controlled, reprogrammable, multipurpose, manipulator programmable in three or more axes, which may be either fixed in place or mobile for use in industrial automation applications." This definition is used by the International Federation of Robotics, the European Robotics Research Network (EURON), and many national standards committees.

The Robotics Institute of America (RIA) uses a broader definition: a robot is a "re-programmable multi-functional manipulator designed to move materials, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks". The RIA subdivides robots into four classes: devices that manipulate objects with manual control, automated devices that manipulate objects with predetermined cycles, programmable and servo-controlled robots with continuous point-to-point trajectories, and robots of this last type which also acquire information from the environment and move intelligently in response.

There is no one definition of robot which satisfies everyone, and many people have their own. For example, Joseph Engelberger, a pioneer in industrial robotics, once remarked: "I can't define a robot, but I know one when I see one." According to Encyclopaedia Britannica, a robot is "any automatically operated machine that replaces human effort, though it may not resemble human beings in appearance or perform functions in a humanlike manner". Merriam-Webster describes a robot as a "machine that looks like a human being and performs various complex acts (as walking or talking) of a human being", or a "device that automatically performs complicated often repetitive tasks", or a "mechanism guided by automatic controls".