Uncontrolled Airspace

Airspace in which aircraft are not subject to controlled airspace (Class A, B, C, D, or E) separation criteria. (PCG definition).

Class G airspace that has not been designated as Class A, B, C, D, or E. It is airspace in which air traffic control has no authority or responsibility to control air traffic; however, pilots should remember there are VFR minimums which apply to this airspace. (PHAK definition).

Source: PCG, Pilot Handbook of Aeronatical Knowledge