Plain English Meaning
A block of controlled airspace that sits out over the ocean, beyond the 12-mile limit of U.S. domestic airspace. It's there so controllers can still provide IFR service to aircraft flying over the water before they reach true open-ocean airspace.
Full Definition
Controlled airspace designated as Class E that extends from 12 nautical miles outward from the U.S. coast, out to where the airspace either meets oceanic airspace or another country's airspace. It exists to provide air traffic control service to instrument flight rules (IFR) operations in international airspace, typically beginning at a specified altitude rather than the surface.