# C4

C4, C04, C.IV, C-4, or C-04 often refers to the explosive. It may refer to:

## Places

* Caldwell 4 or NGC 7023 or Iris Nebula, a reflection nebula in the constellation Cepheus
* Circumferential Road 4 or C-4, an arterial road of Manila, Philippines
* Ken-Ō Expressway, a road in Japan (includes some sections of Shin-Shōnan Bypass)
* Omote-sandō Station, a Tokyo Metro subway station (station number: C-04)
* Wadi C-4, designation for the Tomb of Thutmose II

## People

* C4 (rapper), a rap music producer from Birmingham, England
* Clarence Mitchell IV, American radio host and former politician
* Chris Turner, sometimes credited as Chris Heiner, a.k.a. "C4", Australian musician, part of Modern Day Poets

## Computing

* C4 (conference), a Macintosh software developers conference
* C4 Engine, a next-generation 3D game engine
* C4 model, a graphical notation technique for diagramming software architecture
* Cx4 chip, an add-on microprocessor chip employed by certain Super NES game cartridges (often incorrectly referred to as the C4 chip)
* Controlled collapse chip connection or flip chip, a method for interconnecting semiconductor devices
* VIA C4, a planned design of central processing unit for a personal computer

## Arts, entertainment, and media
### Music

* C4 (American band), a neo-classical metal band set up by Michael Angelo Batio
* C4 (French band), French boyband
* C4 (mixtape), mixtape by American rapper Kendrick Lamar
* C$_4$, scientific pitch notation for the note "Middle C" (261.626 Hz)
* C4 Records, a record label

### Other uses in arts, entertainment and media

* C4 (New Zealand TV channel), a former New Zealand television music channel
* 1. c4, also called the English Opening, a chess opening
* The abbreviation for British TV channel Channel 4.

## Mathematics, science and technology
### Biology

* C4: an EEG electrode site according to the 10-20 system
* Apolipoprotein C4, a protein encoded by the APOC4 gene
* c4 antisense RNA, a non-coding RNA
* ATC code C04 Peripheral vasodilators, a subgroup of the Anatomical Therapeutic Chemical Classification System
* C$_4$ carbon fixation, a pathway for carbon fixation in photosynthesis that produces C4 plants
* Cervical spinal nerve 4, a nerve originating in the neck
* Cervical vertebra 4, one of the cervical vertebrae of the vertebral column
* C04, oral cancer ICD-10 code
* Complement component 4, a protein involved in the intricate complement system, encoded by C4A or C4B gene in humans
* C$_4$ fragments, one of the types of products of catabolism pathways

### Mathematics

* $C_{4}$, the cyclic group of order 4
* C4, the fourth pure "core" module in the Edexcel A-level mathematics examination

### Other uses in science and technology

* C-4 (explosive), a high explosive solid
* C4, butyl-type hydrocarbon chain, a type of four-carbon molecule, especially in C4 reversed-phase chromatography columns
* Cluster 4, an ESA satellite that studies the Earth's magnetosphere over the course of an entire solar cycle
* C-4 Protective Mask, standard issue gas mask of the Canadian Armed Forces.

## Organizations

* C4 (Colombia), a political party in Colombia
* C4, a social welfare non-profit entity organized under section 501(c)(4) of the U.S. Internal Revenue Code
* Churches Covered and Connected in Covenant, a religious association founded by Archbishop LeRoy Bailey Jr.
* Craiova Group, a cooperation project of four European states

## Sports

* C4 (classification), a Paralympic cycling classification
* C-4, professional wrestler Paul Burchill's name for his finishing move, a moonsault uranage
* C4, an abbreviation for a four-man Sprint Canoe, see Canoe racing
* C4, a term used to refer to the UEFA Intertoto Cup, a football competition (mainly used in non-English speaking countries)
* C4 level, a challenge square dance program at the Challenge 4 level

## Stationery

* C4, an international standard paper size (229 × 324 mm), defined in ISO 216
* C4, the envelope size matching the A4 paper size

## Vehicles
### Aircraft

* C-4, the US Army designation of the Ford Trimotor
* AEG C.IV, a German World War I reconnaissance aircraft
* AGO C.IV, a 1917 German reconnaissance aircraft
* C-4 Academe, the military version of Gulfstream I twin turboprop business aircraft
* C-4 Argonaut, a Canadair aircraft derived from the Douglas DC-4
* Cierva C.4, a 1922 Spanish experimental autogyro
* DFW C.IV, a 1916 German reconnaissance aircraft
* Flight Design C4, a four-seat light aircraft
* Fokker C.IV, a 1923 Dutch two-seat reconnaissance aircraft
* Rumpler C.IV, a 1917 German single-engine, two-seater reconnaissance biplane

### Automobiles

* C4, a class of Audi 100 and Audi A6 cars
* Chevrolet Corvette (C4), the fourth production design of the Chevrolet Corvette
* Citroën C4, a car made by Citroën
* Coloni C4, a Formula One car built by Enzo Coloni Racing Car Systems
* Sauber C4, a Sauber sportscar
* Spyker C4, a Spyker car

### Locomotives

* Bavarian C IV, an 1884 German steam locomotive
* GS&WR Class C4, a Great Southern and Western Railway Irish steam locomotive
* LNER Class C4, a class of British steam locomotives

### Ships

* HMS C4, a British C class submarine of the Royal Navy
* Type C4 ship, merchant cargo ships of United States Maritime Commission "C" design
* USS C-4 (SS-15), a United States C class submarine of the United States Navy
* USS Philadelphia (C-4), a protected cruiser of the United States Navy

### Vehicle components

* Ford C4 transmission, an automatic transmission
* Menasco C4, a 1930s 4-cylinder, air-cooled, in-line, inverted, aero-engine

## Weapons

* C-4 (explosive), a type of plastic explosive
* Hafdasa C-4, an Argentine submachine gun

## Other uses

* C4, a variation of Command and control, meaning "Command, Control, Communications and Computers"
* C4, the monogram of Christian IV of Denmark, used in the city arms of Kristianstad, Sweden since 1622
* C4 Extreme, a sports nutrition supplement product line by Cellucor, which includes C4 energy drinks.