The word "fighter" did not become the official English term for such aircraft until after World War I. In Great Britain's Royal Flying Corps – later the Royal Air Force – these aircraft continued to be called "scouts" into the early 1920s. The U.S. Army called their fighters "pursuit" aircraft (reflected by their designation in the "P" series) from 1916 until the late 1940s. In the French, Portuguese and German languages the term used (and still in use) literally means "hunter". This has been followed in most other languages, an exception being Russian, in which the fighter is called "истребитель" (pronounced "istrebitel"), meaning "The Fighter".

Although the term "fighter" technically refers to aircraft designed to shoot down other aircraft, such designs are often also useful as multirole fighter-bombers and sometimes lighter, fighter-sized tactical ground-attack aircraft. For example, in World War II the US Navy would later favor fighters over dedicated dive bombers, and the P-47 Thunderbolt would be favored for ground attack. The controversial F-111 would be employed as a strike bomber as the fighter variant was abandoned. Bombers generally refer to long-range strategic or theater bombing roles. This blurring follows the use of fighters from their earliest days for "attack" or "strike" operations against enemy troops, field positions, vehicles, and facilities by means of strafing or dropping of bombs or incendiaries.

Some of the most expensive fighters such as the F-14 Tomcat, F-22 Raptor and F-15 Eagle were employed as all-weather interceptors as well as air superiority combat aircraft, only developing air-to-ground roles late in their careers. Multirole fighter-bombers such as the F/A-18 Hornet are often less expensive and tasked (and in this case, given an F/A designation) with ground attack as part of a "high-low mix", or in the case of the Super Hornet, replacing a range of specialized aircraft types.

Fighters were developed in response to the fledgling use of aircraft and dirigibles in World War I for reconnaissance and ground-attack roles. Early fighters were very small and lightly armed by later standards, and were mostly biplanes. As aerial warfare became increasingly important, so did control of the airspace. By World War II, fighters were predominantly all-metal monoplanes with wing-mounted batteries of cannons or machine guns. By the end of the war, turbojet engines were already beginning to replace piston engines as the means of propulsion, and increasingly sophisticated refinements to armament were already appearing.

Modern jet fighters are predominantly powered by one or two turbofan engines, and are equipped with a radar as the primary method of target acquisition. Armament consists primarily of air-to-air missiles (from as few as two on some lightweight day fighters to as many as eight or twelve on air superiority fighters like the Sukhoi Su-27 or Boeing F-15 Eagle), with a cannon as backup armament (typically between 20 and 30 mm in caliber); however, they can also employ air-to-surface missiles, as well as guided and unguided bombs.

The word "fighter" was first used to describe a two-seater aircraft with sufficient lift to carry a machine gun and its operator as well as the pilot. The first such "fighters" belonged to the "gunbus" series of experimental gun carriers of the British Vickers company which culminated in the Vickers F.B.5 Gunbus of 1914. The main drawback of this type of aircraft was its lack of speed. It was quickly realized that an aircraft intended to destroy its kind in the air needed at least to be fast enough to catch its quarry.

Fortunately another type of military aircraft already existed, which was to form the basis for an effective "fighter" in the modern sense of the word. It was based on the small fast aircraft developed before the war for such air races as the Gordon Bennett Cup and Schneider Trophy. The military scout airplane was not expected to be able to carry serious armament, but rather to rely on its speed to be able to reach the location it was required to "scout" or reconnoiter and then return quickly to report – while at the same time making itself a difficult target for anti-aircraft artillery or enemy gun-carrying aircraft. British scout aircraft in this sense included the Sopwith Tabloid and Bristol Scout; French equivalents included the light, fast Morane-Saulnier N.

In practice, soon after the actual commencement of the war, the pilots of small scout aircraft began to arm themselves with pistols, carbines, grenades, and an assortment of improvised weapons with which to attack enemy aircraft. It was inevitable that sooner or later means of effectively arming "scouts" would be devised. One method was to build a "pusher" scout such as the Airco DH.2, with the propeller mounted behind the pilot. The main drawback was that the high drag of a pusher type's tail structure meant that it was bound to be slower than an otherwise similar "tractor" aircraft. The other approach was to mount the machine gun armament on a tractor-type airplane in a manner that enabled the gun to fire outside the arc of the propeller.

Only two configuration options were practical initially for tractor aircraft. One involved having a second crew member added behind the pilot to aim and fire a swivel-mounted machine gun at enemy airplanes. However, this limited the area of coverage chiefly to the rear hemisphere, and the inability to effectively coordinate the pilot's maneuvering with the gunner's aiming, which reduced the accuracy and efficacy of the gunnery. This option was chiefly employed as a defensive measure on two seater reconnaissance aircraft from 1915 on. The alternative configuration mounted a gun on the upper wing to fire over the propeller arc. While more effective for offensive combat, since the pilot could move and aim the guns as a unit, this placement made determining the proper aim point more difficult. Furthermore, this location made it nearly impossible for a pilot to maneuver his aircraft and have access to the gun's breech – a very important consideration, given the tendency of early machine guns to jam – hence this was a stopgap solution. Nevertheless, a machine gun firing over the propeller arc did have some advantages, and was to remain in service from 1915 (Nieuport 11) until 1918 (Royal Aircraft Factory S.E.5). The British Foster mounting was specifically designed for this kind of application.

The need to arm a tractor scout with a forward-firing gun whose bullets passed through the propeller arc was evident even before the outbreak of war, and its approach motivated inventors in both France and Germany to devise a practical synchronization gear that could time the firing of the individual rounds to when the propeller was not in the way. Franz Schneider, a Swiss engineer, had patented such a device in Germany in 1913, but his original work was not followed up. French aircraft designer Raymond Saulnier patented a practical device in April 1914, but trials were unsuccessful because of the propensity of the machine gun employed to hang fire due to unreliable ammunition.