Unilateral means on one side.
The terms unilateral is see frequently in discussions of Migraine attacks and cluster headaches, both of which tend to occur on one side of the head.
You can read more about unilateral characteristics of and other symptoms of Migraines and cluster headaches in
Teri Robert is a leading patient educator and advocate and the author of Living Well with Migraine Disease and Headaches. A co-founder of the Alliance for Headache Disorders Advocacy and the American Headache and Migraine Association, she received the National Headache Foundation’s Patient Partners Award and a Distinguished Service Award from the American Headache Society. Teri can be found on her website, and blog, Facebook, Twitter, StumbleUpon, Pinterest, LinkedIn, and Google+.