What is the airspace of defined dimensions located three miles from the coast called?

The airspace located three miles from the coast is referred to as a Warning Area. This type of airspace is established to warn non-participating pilots of activities that may be hazardous to them, such as military training or operations. Warning areas can extend three nautical miles from the coastline outward and can encompass various altitudes, meaning that while they may be over international waters, they are close enough to land to require advisories for safety.

In this context, it is important to understand that while restricted areas, Class G airspace, and Class D airspace have their specific applications and rules, they do not specifically address the safety needs associated with airspace located close to the coast that may involve hazardous activities in international or adjacent areas. Restricted areas may be similar but are often related to specific governmental activities, whereas Class G airspace is uncontrolled and Class D airspace pertains typically to areas around airports with air traffic control. Thus, the defining characteristics and purpose of Warning Areas make it the correct answer for airspace located three miles offshore.