A4 most often refers to: * A4 paper, 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 This article gives an overview of the aquatic communities in the British National Vegetation Classification system. Introduction The aquatic communities of the NVC were described in Volume 4 of ''British Plant Communities'', first published in 1 ...

Combretastatin A-4 Combretastatin A-4 is a combretastatin and a stilbenoid. It can be isolated from '' Combretum caffrum'', the Eastern Cape South African bushwillow tree or in '' Combretum leprosum'', the mofumbo, a species found in Brazil. Function Tubulin repre ...

, a stilbenoid chemical compound * ''A''₄, the alternating group 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 Rhodopsin-like receptors are a family of proteins that comprise the largest group of G protein-coupled receptors. Scope G-protein-coupled receptors, GPCRs, constitute a vast protein family that encompasses a wide range of functions (including ...

subfamily

Medicine

ATC code A04 A04A Antiemetics and antinauseants A04AA Serotonin (5-HT3) antagonists :A04AA01 Ondansetron :A04AA02 Granisetron :A04AA03 Tropisetron :A04AA04 Dolasetron :A04AA05 Palonosetron :A04AA55 Palonosetron, combinations A04AD Other antiemetics :A04AD01 S ...

''Antiemetics and antinauseants'', a subgroup of the Anatomical Therapeutic Chemical Classification System * Lipoxin A4, a lipoxin *

Androstenedione Androstenedione, or 4-androstenedione (abbreviated as A4 or Δ4-dione), also known as androst-4-ene-3,17-dione, is an endogenous weak androgen steroid hormone and intermediate in the biosynthesis of estrone and of testosterone from dehydroepia ...

, an androgen steroid hormone

Transportation

Aeronautics and astronautics

* "A-4 Helldiver", the civil version of the Curtiss Falcon an attack aircraft manufactured by Curtiss Aircraft Company * Douglas A-4 Skyhawk, a 1954 attack aircraft manufactured by Douglas Aircraft Company *

Breda A.4 The Breda A.4 was a biplane Trainer (aircraft), trainer produced in Italy in the mid-1920s. It was of conventional configuration with a two-bay Stagger (aviation), unstaggered wing cellule and seating for the pilot and instructor in tandem open c ...

, a 1926 Italian biplane trainer aircraft * '' Aggregat-4'', the technical name for V-2 ballistic missile * A4,

Southern Winds Airlines Southern Winds Airlines (also known as ''SW Airlines'') was an Argentine commercial air carrier that operated from 1996 until 2005. Southern Winds was founded by Juan Maggio, who served as president of the company. History Initially a domestic ...

, the defunct Argentine airline, as its IATA code * A4, Azimuth (airline), 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 increa ...

, an 1852 German steam locomotive model *

LNER Class A4 The Class A4 is a class of streamlined 4-6-2 steam locomotive designed by Nigel Gresley for the London and North Eastern Railway in 1935. Their streamlined design gave them high-speed capability as well as making them instantly recognisable, ...

, 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 is a subway station on the Toei Asakusa Line, operated by the Tokyo Metropolitan Bureau of Transportation. It is located in Shinagawa, Tokyo, Japan. Its number is A-04. Station layout Togoshi has one platform serving two tracks. Platform 1 is f ...

, 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, 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. Complete Formula One results (key Key or The Key may refer to: Common meanings * Key (cryptography), a piece of information that con ...

, 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 ...

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 Nickelsd ...

* 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 developed ...

rocket * A4, the designation for air force headquarters in the NATO

continental staff system A military staff or general staff (also referred to as army staff, navy staff, or air staff within the individual services) is a group of officers, enlisted and civilian staff who serve the commander of a division or other large military u ...

concerned with logistics ** In the United Kingdom, the A4 Air Logistics branch of the Joint Force Air Component Headquarters * 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 T ...

(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) * Douglas A-4 Skyhawk, an American attack aircraft introduced in 1956 * M16A4, a variant of the American M16 rifle *

Leopard 1A4 The Leopard 1 (also styled Leopard I, before the Leopard 2 simply known as Leopard) is a main battle tank designed and produced by Porsche in West Germany that first entered service in 1965. Developed in an era when HEAT warheads were thought to ...

, 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, 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 unit ...

, a microprocessor *

Samsung Galaxy A04 The Samsung Galaxy A04 is a series of Android smartphones manufactured by Samsung Electronics. It was announced on August 24, 2022. Specifications Hardware The Samsung Galaxy A04 is equipped with a 6.5 in PLS LCD capacitive touchscreen with ...

, a smartphone manufactured by Samsung Electronics

Other uses

* A4 (classification), 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 the ...

, the use of the musical note A to reference musical pitch * A04, Encyclopaedia of Chess Openings code for Réti Opening * A4, a

grade (climbing) In rock climbing, mountaineering, and other climbing disciplines, climbers give a grade to a climbing route or boulder problem, intended to describe concisely the difficulty and danger of climbing it. Different types of climbing (such as sport ...

* 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