Definition
OFFSHORE/CONTROL AIRSPACE AREA
That portion of airspace between the U.S. 12 NM limit and the oceanic CTA/FIR boundary within which air traffic control is exercised. These areas are established to provide air traffic control services. Offshore/Control Airspace Areas may be classified as either Class A airspace or Class E airspace.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).