An electromechanical device which is capable of reacting in some way to its environment, and take autonomous decisions or actions in order to achieve a specific task.
This means that a toaster, a lamp, or a car would not be considered as robots since they have no way of perceiving their environment. On the other hand, a vacuum cleaner that can navigate around a room, or a solar panel that seeks the sun, can be considered as a robotic system.