An aircraft is a vehicle which is able to fly through the Earth's atmosphere or through any other atmosphere.

Manned aircraft are flown by a pilot. Until the 1960s, unmanned aircraft were called drones. During the 1960s, the U.S. military brought the term remotely piloted vehicle (RPV) into use. More recently the term unmanned aerial vehicle (UAV) has become common.

Lighter than air—aerostats

Aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low density gas such as helium, hydrogen or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces.

Small hot air balloons called sky lanterns date back to the 3rd century BC and were only the second type of aircraft to fly, the first being kites.

Originally a balloon was any aerostat, while the term airship was used for large powered aircraft designs—usually fixed-wing—though none had yet been built. The advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by a rigid outer framework and separate aerodynamic skin surrounding the gas bags, were produced, the Zeppelins being the largest and most famous. There were still no aeroplanes or non-rigid balloons large enough to be called airships, so "airship" came to be synonymous with these monsters. Then several accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a "balloon" is an unpowered aerostat, whilst an "airship" is a powered one.

A powered, steerable aerostat is called a dirigible. Sometimes this term is applied only to non-rigid balloons, and sometimes dirigible balloon is regarded as the definition of an airship (which may then be rigid or non-rigid). Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back. These soon became known as blimps. During the Second World War, this shape was widely adopted for tethered balloons; in windy weather this both reduces the strain on the tether and stabilizes the balloon. The nickname blimp was adopted along with the shape. In modern times any small dirigible or airship is called a blimp, though a blimp may be unpowered as well as powered.

Heavier than air—aerodynes

Heavier-than-air aircraft must find some way to push air or gas downwards, so that a reaction occurs (by Newton's laws of motion) to push the aircraft upwards. This dynamic movement through the air is the origin of the term aerodyne. There are two ways to produce dynamic upthrust: aerodynamic lift, and powered lift in the form of engine thrust.