Vibration motors are used for haptic feedback.
Most vibration motors have an Eccentric Rotating Mass, this is the weight that is mounted on the shaft that when rotating produces the vibration. There are also vibration motors that are based on the same principle as a loudspeaker these are called Linear Resonant Actuators.
Typical application areas are mobile phones, game controllers, and in general systems in which feedback should be less obtrusive.
Notice: many vibration motors are made for mobile application and have an input voltage of 3V or less. For 5V application apply a suitable resistor in series.