i reckon a robot is something that can respond to its environment and respond to do that by doing something.
i looked on wikipedia ( http://en.wikipedia.org/wiki/Robot
)and found this:
A robot is an artificial or virtual agent which in the physical form gives the appearance of being alive.
The artificial form (the physical agent) is an electro-mechanical or bio-mechanical device or group of devices that can perform autonomous or preprogrammed tasks while interacting with its surrounding environment using sensors. A telerobot may act under the direct control of a human, such as the robotic arm on a space shuttle, or autonomously under the control of a programmed computer. Robots may be used to perform tasks that are too dangerous or difficult for humans, such as radioactive waste clean-up, or may be used to automate mindless repetitive tasks that should be performed with more precision by a robot than by a human, such as automobile production.
The virtual form is a software-based agent.
Physical robots take on many different forms, ranging from humanoid, which mimic the human form and way of moving, to industrial, whose appearance is dictated by the function they are to perform. Robots can be grouped generally as mobile robots (eg. autonomous vehicles), manipulator robots (eg. industrial robots) and self reconfigurable robots, which can conform themselves to the task at hand. Robots may be controlled directly by a human, such as remotely-controlled bomb-disposal robots and robotic arms; or may act according to their own decision making ability, provided by artificial intelligence. However, the majority of robots fall in-between these extremes, being controlled by pre-programmed computers. Such robots may include feedback loops such that they can interact with their environment, but do not display actual intelligence. "Robot" is also used in a general sense to mean any machine that mimics the actions of a human (biomimicry), in the physical sense or in the mental sense.