D4

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

Science and medicine

22-Dihydroergocalciferol, 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, a human gene
Octamethylcyclotetrasiloxane, called D₄

Dihedral group of order 4, otherwise known as the Klein four-group
Dihedral group of order 8, the symmetry group of a regular 4-gon
D₄ (root system)
In the context of tabletop role-plyaing games might mean "dice 4", referring to Tetrahedron, a regular polyhedron with four faces

D4 (programming language), 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

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

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

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, a punk rock band from Minneapolis, Minnesota

Nikon D4, a flagship DSLR from Nikon
Caterpillar D4 a small crawler type tractor built by Caterpillar Inc.
HMAS Voyager (D04), a 1949 Australian Navy destroyer
HMS D4, a 1911 British submarine
Motorway D4 (Slovakia), a motorway in southwestern Slovakia
Peugeot D4, a French van sold between 1955 and 1965
Dublin 4, a Dublin postcode
d4, a 4-sided die
d4, the second most popular opening move in chess; begins the Queen's Pawn Game
D4, IATA code for Alidaunia airline
D4, commonly used jargon by fans for Ddu-Du Ddu-Du, a song by K-Pop group Blackpink.