D4, D.IV, d4 or variants may refer to:

Science and medicine

22-Dihydroergocalciferol 22-Dihydroergocalciferol is a form of vitamin D, also known as vitamin D4. It has the systematic name (5''Z'',7''E'')-(3''S'')-9,10-seco-5,7,10(19)-ergostatrien-3-ol. Vitamin D4 is found in certain mushrooms, being produced from ergosta-5,7-dien ...

, vitamin D₄ * D4-isoprostane, a type of isoprostane * ATC code D04, ''Antipruritics, including antihistamines, anesthetics, etc.'', a subgroup of the Anatomical Therapeutic Chemical Classification System * D04, Carcinoma in situ of skin ICD-10 code *

Dopamine receptor D4 The dopamine receptor D4 is a dopamine D2-like G protein-coupled receptor encoded by the gene on chromosome 11 at 11p15.5. The structure of DRD4 has been reported in complex with the antipsychotic drug nemonapride. As with other dopamine ...

, a human gene *

Octamethylcyclotetrasiloxane Octamethylcyclotetrasiloxane, also called D4, is an organosilicon compound and one of a number of cyclic siloxanes (cyclomethicones). It is a colorless viscous liquid with a high boiling point. It has historically been used on a large scale in pe ...

, called D₄

Mathematics

* Dihedral group of order 4, otherwise known as the

Klein four-group In mathematics, the Klein four-group is an abelian group with four elements, in which each element is Involution (mathematics), self-inverse (composing it with itself produces the identity) and in which composing any two of the three non-identi ...

* Dihedral group of order 8, the symmetry group of a regular 4-gon * D₄ (root system)

Technology and computing

D4 (programming language) Dataphor is an open-source truly-relational database management system (RDBMS) and its accompanying user interface technologies, which together are designed to provide highly declarative software application development. The Dataphor Server has ...

, a programming language of the Dataphor system * D4 video connector, a type of analog video connector found on Japanese consumer electronics * D4 framing standard, a framing standard for traditional time-division multiplexing

Aircraft

* Albatros D.IV, a World War I experimental German fighter aircraft * Auster D.4, a 1960 two-seat British light aircraft * Dewoitine D.4, a

Dewoitine Constructions Aéronautiques Émile Dewoitine was a French aircraft manufacturer established in Toulouse by Émile Dewoitine in October 1920. The company's initial products were a range of metal parasol-wing fighters, which were largely ignored by ...

aircraft *

Dunne D.4 The Dunne D.1, was an experimental tailless aircraft, tailless aircraft built in the UK in 1907. It comprised a main unit which could be flown as a glider, to which a chassis unit with power train could be added. The glider achieved a short flig ...

, a 1907 British experimental aircraft * Fokker D.IV, a World War I German fighter biplane * Phönix D.IV, a KuKLFT D-class designation aircraft * Schütte-Lanz D.IV, a 1917 German fighter prototype aircraft * Siemens-Schuckert D.IV, a 1918 German fighter aircraft

Transport

Rail

* Bavarian D IV, an 1878 German tank locomotive model * Bavarian D IV (Ostbahn), an 1867 German steam locomotive model * D4, the tank engine variant of the Victorian Railways Dd class locomotive in Australia * GSWRI Class D4, a Great Southern and Western Railway Irish steam locomotive * LNER Class D4, a class of British steam locomotives * PRR D4, an 1873 American steam locomotive model * SP&S Class D-4, a Spokane, Portland and Seattle Railway locomotive

Road

D4 motorway (Czech Republic) D4 motorway (), until 31 December 2015 formerly Limited-access highway, Expressway R4 () is a Controlled-access highway, motorway running from Prague in the Czech Republic, in a southwesterly direction. Some of the sections are managed through th ...

, a motorway in the Czech Republic * D4 motorway (Slovakia), a motorway in Slovakia

Engines

* Mercedes D.IV, a World War I German 8-cylinder, liquid-cooled inline aircraft engine * Mercedes D.IVa, a 1917 German 6-cylinder, water-cooled, inline aircraft engine

Media and entertainment

* The D4, a rock band from Auckland, New Zealand * '' D4 Princess'', a 1999 Japanese manga series * '' D4: Dark Dreams Don't Die'', a video game by Hidetaka Suehiro for the Xbox One and PC * ''D4'' (film), by Darrin Dickerson * '' D4 - Get Up and Dance'', an Indian dance fiction television series * '' Diablo IV'', an action role-playing game by Blizzard Entertainment *

Dillinger Four Dillinger Four (sometimes abbreviated as D4) is an American punk rock band formed in 1994 in Minneapolis, Minnesota. They have released four full-length studio albums. Since 1996, the band's lineup has been Patrick Costello on bass guitar and v ...

, a punk rock band from Minneapolis, Minnesota

Other uses

Nikon D4 The Nikon D4 is a 16.2-megapixel professional-grade full frame ( 35mm) digital single-lens reflex camera ( DSLR) announced by Nikon Corporation on 6 January 2012. It succeeds the Nikon D3S and introduces a number of improvements including a 16 ...

, a flagship DSLR from Nikon *

Caterpillar D4 The Caterpillar D4 track-type tractor is a small bulldozer manufactured by Caterpillar Inc. Caterpillar first introduced the RD4 in 1936, as the diesel follow on to the successful CAT 30 gas model. The RD4 originally weighed in at , and used Cat ...

a small crawler type tractor built by Caterpillar Inc. * , a 1949 Australian Navy destroyer * , a 1911 British submarine *

Motorway D4 (Slovakia) D4 motorway () is a Slovakia, Slovak motorway which, when completed, will form the outer ring road around Bratislava, speed up access to motorway networks and partially reduce traffic on the road network in the catchment areas of Bratislava. The ...

, a motorway in southwestern Slovakia * Peugeot D4, a French van sold between 1955 and 1965 *

Dublin 4 Dublin 4, also rendered as D4 and D04, is a historic postal district of Dublin, Ireland including Baggot Street Upper, the southernmost fringes of the Dublin Docklands, and the suburbs of Ballsbridge, Donnybrook, Irishtown, Merrion, Ringsend ...

, a Dublin postcode * d4, a

4-sided die Four-sided dice, abbreviated d4, are often used in tabletop role-playing games to obtain random integers in the range 1–4. Forms Several forms exist of this die. One is a regular tetrahedron, which is a triangular pyramid with four equilatera ...

* d4, the second most popular opening move in chess; begins the

Queen's Pawn Game The Queen's Pawn Game is any chess opening starting with the move: : 1. d4 It is the second-most popular opening move after 1.e4 (King's Pawn Game). Terminology The term "Queen's Pawn Game" is usually used to describe openings beginning wit ...

* D4, IATA code for Alidaunia airline * D4, commonly used jargon by fans for Ddu-Du Ddu-Du, a song by K-Pop group

Blackpink Blackpink (, stylized in all caps or as BLɅϽKPIИK) is a South Korean girl group formed by YG Entertainment. The group is composed of four members: Jisoo, Jennie (singer), Jennie, Rosé (singer), Rosé, and Lisa (rapper), Lisa. Regarded by ...