What is Headache and what are the causes of headaches?

I've been suffering headaches since I was still in the third level. Until now sometimes these headache disturbs me. I've been researching for the causes of Headaches.
What is Headache?
According to MedicineNet.com that headache is a pain in the head or in the upper neck.
What are the Causes of Headache?
As I have researched from different sources, here are some common causes of headaches

• Not getting enough sleep
• skip meals
• caffeine
• drink too much alcohol
  
• stress
• depression
• anxiety

According to medhelp.org, Tension headaches are in both sides of your head. Migraine headaches are severe accompanied by other symptoms or any disturbances.



Note: These are just only minor causes. There is an explanation of each causes.


References:
MedicineNet.com

medhelp.org