tremor of unknown cause (usually of the hands and head) that develops in older people; often mistaken for Parkinsonism but is not life-threatening and can usually be kept under control
a single pulsation of an oscillation produced by adding two waves of different frequencies; has a frequency equal to the difference between the two oscillations
a vibration of large amplitude produced by a relatively small vibration near the same frequency of vibration as the natural frequency of the resonating system