A common primary headache disorder, characterized by a dull, non-pulsatile, diffuse, band-like (or vice-like) PAIN of mild to moderate intensity in the HEAD; SCALP; or NECK. The subtypes are classified by frequency and severity of symptoms. There is no clear cause even though it has been associated with MUSCLE CONTRACTION and STRESS. (International Classification of Headache Disorders, 2nd ed. Cephalalgia 2004: suppl 1).