General aviation includes almost all civilian uses of aircraft. Aircraft operated by (a) the military or (b) the major airlines, which move passengers or cargo, are usually not included. Even though general aviation refers to civilian aircraft, most of the examples we immediately might think of (i.e. - travel on the major airlines) are not considered general aviation: they are commercial aircraft operations controlled by a common carrier. The key concept is the civilian control for personal or business reasons other than commercial air use.
The FAA lists certified aircraft on the basis of engine size, design, passenger, fuel, and cargo capacity. The increasing popularity of recreational aviation (a subset of general aviation) means that the lists continue to grow every year. Types of recreational aircraft typically include: ultra lights, small aircraft, light sport aircraft, vintage military aircraft and more.
Categories of aircraft (some of which can be converted to and from commercial use) include but are not limited to:
Light Sport Aircraft: this includes most popular small aircraft, e.g. - Aeronca, Piper, etc.
Primary Small Aircraft Category
Restricted Category
Very Light Airplanes
The National Transportation Safety Board (NTSB) has the ability to suggest rules regulating and defining the general aviation industry, which the FAA may choose to accept or reject. The NTSB is important in defining the lines between general aviation and commercial aviation, because it makes separate rules for each group. This also leads to potential conflicts between general aviation and government regulators. The Aircraft Owners and Pilots Association is among the largest and most influential association of general aviation pilots. This group also works to be sure to address what it views as the best safety and operating rules for general aviation as a distinct group of pilots and manufacturers.