Plain English Meaning
The airspace where ATC does not control traffic. Pilots are responsible for separating themselves from other aircraft by seeing and avoiding them, while still following the basic rules for visibility and distance from clouds.
Full Definition
Class G airspace is uncontrolled airspace — the portion of the atmosphere that has not been designated as Class A, B, C, D, or E. Air traffic control has no authority or responsibility over aircraft operating in Class G, though pilots must still comply with applicable visual flight rules and minimum safe altitudes. It typically exists close to the ground in remote or rural areas, often from the up to the of the overlying .