A headache is a common health condition characterized by pain or discomfort in the head or upper neck. It can range from mild to severe and may be accompanied by other symptoms such as sensitivity to light or sound, nausea, or fatigue. The document discusses the main types of headaches including tension headaches, migraines, cluster headaches, and sinus headaches. It also examines potential causes of headaches along with treatment and management strategies for different types of headaches.