A4 most often refers to: *

A4 paper ISO 216 is an international standard for paper sizes, used around the world except in North America and parts of Latin America. The standard defines the "A", "B" and "C" series of paper sizes, including A4, the most commonly available paper size ...

, a paper size defined by the ISO 216 standard, measuring 210 × 297 mm A4 and variants may also refer to:

Science and mathematics

* British NVC community A4 (''Hydrocharis morsus-ranae - Stratiotes aloides'' community), one type of Aquatic communities in the British National Vegetation Classification system * Combretastatin A-4, a stilbenoid chemical compound * ''A''₄, the

alternating group In mathematics, an alternating group is the group of even permutations of a finite set. The alternating group on a set of elements is called the alternating group of degree , or the alternating group on letters and denoted by or Basic pr ...

on four elements * A4, a type of stainless steel, as defined by ISO 3506, equivalent to SAE steel grade 316L * Subfamily A4, a rhodopsin-like receptors subfamily

Medicine

* ATC code A04 ''Antiemetics and antinauseants'', a subgroup of the Anatomical Therapeutic Chemical Classification System *

Lipoxin A4 A lipoxin (LX or Lx), an acronym for lipoxygenase interaction product, is a bioactive autacoid metabolite of arachidonic acid made by various cell types. They are categorized as nonclassic eicosanoids and members of the specialized pro-resolving ...

, a lipoxin * Androstenedione, an androgen steroid hormone

Transportation

Aeronautics and astronautics

* "A-4 Helldiver", the civil version of the

Curtiss Falcon The Curtiss Falcon was a family of military biplane aircraft built by the American aircraft manufacturer Curtiss Aeroplane and Motor Company during the 1920s. Most saw service as part of the United States Army Air Corps as observation aircraft ...

an attack aircraft manufactured by Curtiss Aircraft Company *

Douglas A-4 Skyhawk The Douglas A-4 Skyhawk is a single-seat subsonic carrier-capable light attack aircraft developed for the United States Navy and United States Marine Corps in the early 1950s. The delta-winged, single turbojet engined Skyhawk was designed a ...

, a 1954 attack aircraft manufactured by Douglas Aircraft Company * Breda A.4, a 1926 Italian biplane trainer aircraft * '' Aggregat-4'', the technical name for V-2 ballistic missile * A4, Southern Winds Airlines, the defunct Argentine airline, as its IATA code * A4,

Azimuth (airline) Azimuth (russian: АО «АЗИМУТ», translit=, link=no, branding itself as azimuth) is a Russian joint-stock company airline based in Platov International Airport in Rostov-on-Don, the capital of Rostov Oblast. History Due to the merger o ...

, as its current IATA code *

A-004 A-004 was the sixth and final test of the Apollo launch escape vehicle and the first flight of a Block I production-type Apollo Command/Service Module. Objectives Mission A-004 was uncrewed and was conducted to demonstrate that # The launch e ...

, the sixth and final abort test of the Apollo spacecraft * S.A-4 or A.4, 1915 French reconnaissance fighter built by SPAD

Railways

Bavarian A IV Bavarian A IV engines were German 2-2-2 steam locomotives with the Royal Bavarian State Railways (''Königlich Bayerische Staatsbahn''). The vehicles were developed for night journeys and operations on the North-South Railway. In order to incre ...

, an 1852 German steam locomotive model * LNER Class A4, a class of steam locomotives, including the famous ''Mallard'' * PRR A4, an American

Pennsylvania Railroad locomotive classification Locomotive classification on the Pennsylvania Railroad took several forms. Early on, steam locomotives were given single-letter classes. As the 26 letters were quickly assigned, that scheme was abandoned for a more complex system. This was used fo ...

* Togoshi Station, number A-04 on the Toei Asakusa Line

Ships

* ''A-4'', , a ''Plunger''-class submarine of the United States Navy, which was renamed ''A-4'' on 17 November 1911 * , a 1978 Royal New Zealand Navy ''Moa''-class inshore patrol vessel * , an A-class submarine of the Royal Navy * , a Belgian naval patrol vessel of World War II

Other vehicles

Audi A4 The Audi A4 is a line of compact executive cars produced since 1994 by the German car manufacturer Audi, a subsidiary of the Volkswagen Group. The A4 has been built in five generations and is based on the Volkswagen Group B platform. The first ...

, a luxury compact executive car manufactured by Audi, introduced in 1994 *

Arrows A4 The Arrows A4 was the car which the Arrows Formula One team used to compete in the 1982 Formula One season The 1982 FIA Formula One World Championship was the 36th season of FIA Formula One motor racing. It included two competitions run ove ...

, a 1982 British racing car * Prussian A 4, a 1913 German

railbus A railbus is a lightweight passenger railcar that shares many aspects of its construction with a bus, typically having a bus (original or modified) body and four wheels on a fixed base, instead of on bogies. Originally designed and developed d ...

Roads and routes

List of A4 roads This is a list of roads designated A4. A4 is the name of several roads: * A004 road (Argentina), a road connecting Buenos Aires-La Plata highway with the Juan María Gutiérrez circle * A4 motorway (Austria), a road connecting Vienna and Nickels ...

* A4, a Metrobus route in Washington, D.C.

Military

* A4, the model number of the World War II-era German

V-2 The V-2 (german: Vergeltungswaffe 2, lit=Retaliation Weapon 2), with the technical name ''Aggregat 4'' (A-4), was the world’s first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was develope ...

rocket * A4, the designation for air force headquarters in the NATO continental staff system concerned with logistics ** In the United Kingdom, the A4 Air Logistics branch of the

Joint Force Air Component Headquarters The Joint Force Air Component Headquarters (JFACHQ) is the United Kingdom's deployable air command and control unit. The JFACHQ is run by the Royal Air Force with representation from the other services. The JFACHQ has members from the operatio ...

* A 4, see

List of Swedish regiments This is a list of Swedish regiments and other military units ( divisions, brigades, battalions, companies) that have existed since the 16th century. Most formations have changed names several times during their existence. Listed here are commonly ...

for A4, a Swedish designation (4th Artillery Regiment) that has been used by: **

Gotlands artilleriregemente The Gotland Artillery Regiment ( sv, Gotlands artilleriregemente, designation A 7) was a Swedish Army artillery regiment that was in active service between 1811 and 2000. The regiment was based in Visby as part of the Gotland Garrison. History ...

(unknown–1892) **

Norrlands artilleriregemente The Norrland Artillery Regiment ( sv, Norrlands artilleriregemente), designation A 4, was a Swedish Army artillery regiment that traced its origins back to the 19th century. The regiment's soldiers were originally recruited from the provinces of ...

(1893–1997) *

, an American attack aircraft introduced in 1956 *

M16A4 The M16 rifle (officially designated Rifle, Caliber 5.56 mm, M16) is a family of military rifles adapted from the ArmaLite AR-15 rifle for the United States military. The original M16 rifle was a 5.56×45mm automatic rifle with a 20-roun ...

, a variant of the American M16 rifle * Leopard 1A4, a variant of the German Leopard 1 main battle tank *

Leopard 2A4 The Leopard 2 is a 3rd generation main battle tank originally developed by Krauss-Maffei in the 1970s for the West German army. The tank first entered service in 1979 and succeeded the earlier Leopard 1 as the main battle tank of the West Germ ...

, a variant of the German Leopard 2 main battle tank

Computing

Apple A4 The Apple A4 is a 32-bit package on package (PoP) system on a chip (SoC) designed by Apple Inc. and manufactured by Samsung. It was the first SoC Apple designed in-house. The first product to feature the A4 was the first-generation iPad, follo ...

, a microprocessor used in some Apple products *

AMD A4 AMD Accelerated Processing Unit (APU), formerly known as Fusion, is a series of 64-bit microprocessors from Advanced Micro Devices (AMD), combining a general-purpose AMD64 central processing unit ( CPU) and integrated graphics processing uni ...

, a microprocessor * Samsung Galaxy A04, a smartphone manufactured by Samsung Electronics

Other uses

A4 (classification) A4 is an amputee sport classification used by the International Sports Organization for the Disabled (ISOD).for people with acquired or congenital amputations. People in this class have one leg amputated below the knee. Their amputations impact t ...

, an amputee sport classification * A4 or A₄, the musical note La or A in the fourth octave *

A440 (pitch standard) A440 (also known as Stuttgart pitch) is the musical pitch corresponding to an audio frequency of 440 Hz, which serves as a tuning standard for the musical note of A above middle C, or A4 in scientific pitch notation. It is standardized by th ...

, the use of the musical note A to reference musical pitch * A04, Encyclopaedia of Chess Openings code for

Réti Opening The Réti Opening is a hypermodern chess opening whose "traditional" or "classic method" begins with the moves: :1. Nf3 d5 :2. c4 White attacks Black's pawn from the , which may occasion 2...dxc4. White may couple this plan with a kingside ...

* A4, a grade (climbing) * A4, the code for permission to use specific land or premises for pubs and bars in town and country planning in the UK * A4 Pod, a family of killer whales living in British Columbia coastal waters * A4, a 1981 component for the ''Scourge of the Slave Lord'' adventure in the ''Dungeons and Dragons'' role playing game * Biu-Mandara A.4 languages, a family of languages spoken in Cameroon and Nigeria