Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Essential tremor ?
    ### Response:
    Essential tremor is the most common movement disorder.  It is characterized by involuntary and rhythmic shaking (tremor), especially in the hands, without any other signs or symptoms. It is distinguished from tremor that results from other disorders or known causes, such as tremors seen with Parkinson disease or head trauma.
    