A4 commonly refers to:
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A4 paper, a paper size defined by the ISO 216 standard, measuring 210 × 297 mm
A4 and variants may also refer to:
Science and technology
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British NVC community A4 ( Hydrocharis morsus-ranae - Stratiotes aloides community), one type of Aquatic communities in the British National Vegetation Classification system
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Combretastatin A-4, a stilbenoid chemical compound
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A4, the alternating group on four elements
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A4, a type of stainless steel
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Subfamily A4, a rhodopsin-like receptors subfamily
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Zeolite A-4, a sodium-type molecular sieve also known as 4A
Computing
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Apple A4, a microprocessor used in some Apple products
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AMD A4, a microprocessor
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Samsung Galaxy A04, a smartphone manufactured by Samsung Electronics
Medicine
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ATC code A04 Antiemetics and antinauseants, a subgroup of the Anatomical Therapeutic Chemical Classification System
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Lipoxin A4, a lipoxin
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Androstenedione, an androgen steroid hormone
Transportation
Aeronautics and astronautics
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A-4 Helldiver, the civil version of the Curtiss Falcon an attack aircraft manufactured by Curtiss Aircraft Company
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Douglas A-4 Skyhawk, a 1954 attack aircraft manufactured by Douglas Aircraft Company
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Breda A.4, a 1926 Italian biplane trainer aircraft
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Aggregat-4, the technical name for V-2 ballistic missile
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Southern Winds Airlines (IATA code: A4), a defunct Argentine airline
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Azimuth (airline) (IATA code: A4), a Russian airline
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A-004, the sixth and final abort test of the Apollo spacecraft
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SPAD S.A-4, 1915 French reconnaissance fighter built by SPAD
Railways
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Bavarian A IV, an 1852 German steam locomotive model
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LNER Class A4, a class of steam locomotives, including the famous Mallard
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PRR A4, an American Pennsylvania Railroad locomotive classification
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Togoshi Station (station number A-04), Toei Asakusa Line, Tokyo
Ships
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USS A-4 (SS-5), a Plunger-class submarine of the United States Navy
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HMNZS Kahu (A04), a 1978 Royal New Zealand Navy Moa-class inshore patrol vessel
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HMS A4, an A-class submarine of the Royal Navy
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Belgian ship A4, a Belgian naval patrol vessel of World War II
Other vehicles
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Audi A4, a luxury compact executive car manufactured by Audi, introduced in 1994
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Arrows A4, a 1982 British racing car
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Prussian A 4, a Prussian railbus
Roads and routes
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List of A4 roads
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A4, a Metrobus route in Washington, D.C., US
Military
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A4, the designation for air force headquarters in the NATO continental staff system concerned with logistics
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A4 Air Logistics, a branch of the Joint Force Air Component Headquarters in the UK
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A 4, see List of Swedish regiments for A4, a Swedish designation (4th Artillery Regiment) that has been used by:
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Gotland Artillery Regiment (designation: A 4), until 1892
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Norrland Artillery Regiment (designation: A 4), 1893–1997
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M16A4, a variant of the American M16 rifle
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Leopard 1A4, a variant of the German Leopard 1 main battle tank
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Leopard 2A4, a variant of the German Leopard 2 main battle tank
Other uses
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A4 (classification), an amputee sport classification
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A4 or A4, the musical note La or A in the fourth octave
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A440 (pitch standard), the use of the musical note A to reference musical pitch
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Réti Opening (Encyclopaedia of Chess Openings code: A04)
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A4, a climbing route grade
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A4, the code for permission to use specific land or premises for pubs and bars in town and country planning in the UK
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A4 pod, a family of killer whales living in British Columbia coastal waters
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A4, a 1981 component for the Scourge of the Slave Lord adventure in the Dungeons and Dragons role playing game
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Biu-Mandara A.4 languages, a family of languages spoken in Cameroon and Nigeria
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Vlad A4, Belarusian YouTuber
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A4 Revolution, the 2022 COVID-19 protests in China
See also
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4A (disambiguation)
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A4A (disambiguation)
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AIV (disambiguation)
