Aviation

Aviation is a general term applied to the science of and technology for flying through the air, including not only the operation of civil and military aircraft but also the operation of industries and services that supports it directly (McGraw-Hill Encyclopedia of Science and Technology, 2005¹).

The field of aviation is divided into different categories. The broadest division is that which separates civil aviation from military aviation.

Civil aviation
Civil aviation deals with the operation of aircraft and the provision of air services by civil organizations and for civil purposes. Civil aviation is typical subdivided into other categories depending on their economic purpose (commercial versus private) or on the establishment of a regular service (air transport versus general aviation). Purpose and regular service are not mutually exclusive. Thus, although scheduled air transport is commercial, commercial operations are also common within general aviation.
Air transport, or Airline	Air transport provides scheduled air services for passengers (passenger airlines) or freight (cargo airlines). To fly airlines, a pilot is required to hold a current air transport pilot's license and appropriate ratings. (Image: A cargo airline, FedEx Express —embedded from Wikipedia on 2 April 2010)
General aviation	General aviation is a default category. That is, all air operations and services that are not part of military or air transport operations, are, thus, general aviation. Activities range from parachuting to the training of future commercial pilots, including gliding, private flying, air ambulance, police air surveillance, aerial firefighting, etc. (Image: the general aviation terminal at Raleigh Durham International Airport —embedded from Wikipedia on 2 April 2010)

Commercial aviation	Commercial aviation stands for flights done for profit. Three main criteria are required for commercial aviation: pilots must hold valid commercial pilot's licenses (and appropriate ratings), aircraft must hold valid commercial registrations, and operators must hold authorization for commercial operations. (Image: International airline traffic routes in 2009 —embedded from Wikipedia on 2 April 2010)
Private aviation	Private aviation stands for not-for-profit flying. To fly privately, a pilot is only required to hold a current private pilot's license and appropriate ratings; and not to generate income from his flying. (Image: Aerobatic flying can be done for not-profit, requiring only a PPL —embedded from Wikipedia on 2 April 2010)
Military aviation
Military aviation is the operation of aircraft and the provision of air services by the military, normally for military purposes. Although there couldn't be a classification of military aviation according to purpose or regularity, we could categorize it according to the military branch that uses aviation in their operations.
Air force	The Air Force is the primary air defender of its country and the typical warfare air operator, although it also bombs enemy positions and offers support to ground armies from the air. (Image: RAF Eurofighter Typhoon —embedded from Wikipedia on 2 April 2010)
Army aviation	A country's army may use aviation for attack, transport and support purposes (such as surveillance, rescue missions, etc). Typically, army aviation comprises helicopters and light fixed-wing aircraft. (Image: OH-58D Kiowa and AH-64 Apache helicopters from the 3rd Armored Cavalry Regiment (USA) —embedded from Wikipedia on 2 April 2010)
Maritime aviation	The Coast Guard of a country (if it is a separate military branch from the Navy or the Army) has responsibility for maritime safety, security and stewardship, typically within national waters. The Coast Guard may also use aircraft, such as helicopters, light fixed-wing aircraft and UAVs, for carrying out its duties. (Image: HC-144A Ocean Sentry of the U.S. Coast Guard —embedded from Wikipedia on 2 April 2010)
Naval aviation	Naval aviation is part of the Navy, being prototypically brought near the enemy coast by aircraft carriers. Naval aircraft may be fixed-wing or helicopters, and will have different roles, from offensive warfare to search and rescue, transport, weather observation, reconnaissance, etc. (Image: two aircraft launching from their carrier simultaneously —embedded from Wikipedia on 2 April 2010)