Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Headache ?
    ### Response:
    Almost everyone has had a headache. Headache is the most common form of pain. It's a major reason people miss days at work or school or visit the doctor.    The most common type of headache is a tension headache. Tension headaches are due to tight muscles in your shoulders, neck, scalp and jaw.
    