Tremors are an unintentional, somewhat rhythmic, muscle movements involving to-and-fro movements (oscillations) of one or more parts of the body. They are the most common of all involuntary movements and can affect the hands, arms, head, face, vocal cords, trunk, and legs. Most tremors occur in the hands. In some people, tremors are a symptom of another neurological disorder. The most common form of tremors, however, occur in otherwise healthy people. Although tremors are not life-threatening, they can be embarrassing to some people and make it harder to perform daily tasks.
This answer is based on source information from the National Institute of Neurological Disorders and Stroke.