Robot is 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.
Roboticists develop man-made mechanical devices that can move by themselves, whose motion must be modelled, planned, sensed, actuated and controlled, and whose motion behavior can be influenced by “programming”.
This definition implies that a device can only be called a “robot” if it contains a movable mechanism, influenced by sensing, planning, actuation and control components. Motors and actuators are the devices which make the robot movable. Motors and actuators convert electrical energy into physical motion. The vast majority of actuators produce either rotational or linear motion.
You already know that electric motors are used to “actuate” something in your robot: its wheels, legs, tracks, arms, fingers, sensor turrets, camera, or weapon systems.There are literally dozens of types of electric motors but I've mentioned very short note of the most common types used in amateur robotics. Motors are classified as:
Brushed DC motor
Brushless DC motor
Geared DC motor
DC Linear Actuator
In general, a motor is a device or machine which convert electrical energy to mechanical energy and a motor convert the energy one from to another through magnetic domain. There must be two magnetic flux to produce the mechanical force or energy and from interaction of two magnetic flux always produce some mechanical forces.