A robot is a mechanical or virtual, artificial agent. It is usually an electromechanical system, which, by its appearance or movements, conveys a sense that it has intent or agency of its own. The word robot can refer to both physical robots and virtual software agents, but the latter are usually referred to as bots to differentiate.

While there is still discussion about which machines qualify as robots,a typical robot will have several, though not necessarily all of the following properties
is not 'natural' i.e. artificially created
can sense its environment, and manipulate or interact with things in it has some degree of intelligence or ability to make choices based on the environment, often using automatic control or a preprogrammed sequence
is programmable
moves with one or more axes of rotation or translation
makes dexterous coordinated movements
appears to have intent or agency (See anthropomorphism for examples of ascribing intent to inanimate objects.[5])

Defining characteristics

The last property, the appearance of agency, is important when people are considering whether to call a machine a robot, or just a machine. In general, the more a machine has the appearance of agency, the more it is considered a robot.
Mental agency
For robotic engineers, the physical appearance of a machine is less important than the way its actions are controlled.[6] 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. So the more a machine could feasibly choose to do something different, the more agency it has. For example:
a clockwork car is never considered a robot[7]
a remotely operated vehicle is sometimes considered a robot[8] (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, like the 1990s driverless cars of Ernst Dickmanns, or the entries to the DARPA Grand Challenge, which could sense its environment, and make driving decisions based on this information would quite likely be called 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 looks anthropomorphic or zoomorphic (e.g. ASIMO or Aibo), especially if it is limb-like (e.g. a simple robot arm), or has limbs, or can move around, it would be called a robot.

For example, even if the following examples used the same control architecture:
a player piano is rarely characterized as a robot[9]
a CNC milling machine is very occasionally characterized as a robot.
a factory automation arm is almost always characterized as a robot or 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 robot, a mobile robot or a service robot
a zoomorphic mechanical toy, like Roboraptor, is usually characterized as a robot.[10][11]
a humanoid, like ASIMO, is almost always characterized as a robot or a service robot.
Interestingly, while a 3-axis CNC milling machine may have a very similar or identical control system to a robot arm, it is the arm which is almost always called a robot, while the CNC machine is usually just a machine. Having a limb can make all the difference. Having eyes too gives people a sense that a machine is aware ("the eyes are the windows of the soul"). However, simply being anthropomorphic is not sufficient for something to be called a robot. A robot must do something, whether it is useful work or not. So, for example, a rubber dog chew, shaped like ASIMO, would not be considered a robot.