What's the difference between omega3 and omega4?

Essential fats: Omega 3 fatty acids (fish, seafood, etc) are vital components for many cellular structures and are considered "essential" because the human body cannot synthesize these from scratch, and therefore must be ingested. I've never seen anything about omega 4, but some omega 6 fatty acids (vegetable oils) are also essentual, but are known to be inlammatory, not anti-inflammotory like omega 3.

Organic chemistry: Omega 3 fatty acids consist of carbon atoms which are connected mostly by single bonds and a few double bonds. The 3 indicates at which carbon atom the double bonds begin. They begin at the 3rd c atom for omega 3s and at the 4th c atom in omega 4s. See: http://www.Dhaomega3.Org/overview/structures-of-omega-3-fatty-acids.