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

Technology and computing

• 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

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 aircraft
• Dunne D.4, a 1907 British experimental aircraft
• Fokker D.IV, a World War I German fighter biplane
• LFG Roland D.VI, an aircraft powered by the German Mercedes D.III engine
• 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

Rail transport

• Bavarian D IV, an 1878 German tank locomotive model
• Bavarian D IV (Ostbahn), an 1867 German steam locomotive model
• GSWRI Class D4, a Great Southern and Western Railway Irish steam locomotive
• PRR D4, an 1873 American steam locomotive model
• SP&S Class D-4, a steam locomotives class

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

Other

• Nikon D4, a flagship DSLR from Nikon
• Caterpillar D4 a Small crawler type tractor built by Caterpillar Inc.
• HMAS Voyager (D04), a 1949 Daring class Australian Navy destroyer
• Motorway D4 (Slovakia), a motorway in southwestern Slovakia
• The symmetry group of a square - Examples of groups
• 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 airport
• A model of tractor made by Caterpillar, Inc.