Essential tremor: Uncontrollable shaking (tremor) of the hands and arms and sometimes other parts of the body. Essential tremor is the most common of all movement disorders and is estimated to affect up to 5% of people in the US. In approximately half of cases, essential tremor is inherited in an autosomal dominant manner. Several different genetic defects may play a role in this condition. The degree of severity of symptoms is variable among affected people. It most often affects the hands and arms but may also involve the legs, trunk, head, voice, and chin.