# C3

C3, C-3, C.3, C03, C.III or C-III may refer to:

## Life and biology

* C$_3$ carbon fixation in plants
* C3-convertase, an enzyme
* Complement component 3, a protein of the innate immune system
* Apolipoprotein C3, a human very low density lipoprotein
* ATC code C03 Diuretics, a subgroup of the Anatomical Therapeutic Chemical Classification System
* Castavinol C3, a natural phenolic compound found in red wines
* Cytochrome-c3 hydrogenase, an enzyme
* Haplogroup C-M217, called C3 in older publications
* In human anatomy, C3 may refer to:
** Cervical vertebra 3, one of the cervical vertebrae of the vertebral column
** Cervical spinal nerve 3
* Clinical Cell Culture, a medical technology company
* C03, Malignant neoplasm of gum ICD-10 code
* C3 Collaborating for Health, a health-promotion NGO
* C3: an EEG electrode site according to the 10-20 system

## Military

* C$^3$, Command, control, and communications, a military concept
* C-3 (plastic explosive), a plastic explosive related to C4
* C-3, a United States military designation for the Ford Trimotor
* the designation for several German World War I and World War II armed reconnaissance aircraft
** AEG C.III
** AGO C.III, a reconnaissance biplane of World War I
** Albatros C.III
** DFW C.III, a DFW aircraft
* NAG C.III, an engine powering the Gotha G.IV aircraft
* C-3, a U.S. military transport version of the Martin 4-0-4
* Type C3 submarine (disambiguation), a World War II Imperial Japanese Navy cargo carrier submarine
* Spanish submarine C-3
* HMS C3, a 1906 British C class submarine
* Type C3-class ship, a type of merchant cargo ships of United States Maritime Commission "C" design
* USS C-3 (SS-14), a 1909 United States C class submarine
* USS Baltimore (C-3), an 1888 protected cruiser of the United States Navy
* Garda Crime and Security Branch (CSB), domestic security agency of Ireland's national police, also known as "C3"
* C3 Howitzer, a lengthened variant of the M101 used by the Canadian Armed Forces

## Technology

* C$_3$, characteristic energy, in astrodynamics, a measure of the rocket energy for an interplanetary mission that requires attaining an orbital velocity above escape velocity
* C$_3$, the chemical symbol for
** Tricarbon
** Cyclopropatriene
* C3.ai, an AI company founded by Thomas Siebel
* C3 linearization, a computer science algorithm for resolving the order of method resolution in multiple inheritance conditions
* Delfi-C3, a Dutch CubeSat satellite
* Saturn C-3, a 1960 rocket in the Saturn C series
* Chaos Communication Congress, the biggest annual hacker event in Europe
* Chrysler Comprehensive Compensation System, important in the development of Extreme Programming
* VIA C3, a computer processor
* Creatures 3, a 1999 video game
* Crysis 3, a 2013 video game
* Cluster 3, also known as Samba, an ESA satellite

## Transportation

* Aeronca C-3, an American airplane
* Bavarian C III, a German steam locomotive model
* Bavarian C III (Ostbahn), an 1867 German steam locomotive model
* Chevrolet Corvette (C3), the third production design of the Chevrolet Corvette
* Circumferential Road 3 or C-3, an arterial road of Manila, Philippines
* Cierva C.3, a 1921 Spanish experimental autogyro
* Citroën C3, a car
* Cowin C3, a car
* LB&SCR C3 class, a British LB&SCR locomotive
* London Buses route C3, a Transport for London contracted bus route
* C3 (railcar), a bi-level railcar built by Kawasaki Railcar for the non-electrified branches of the Long Island Rail Road
* Nimrod NRA/C3, a 1983 Group C racing car never achieved
* Yamaha C3, a 2007 liquid cooled 49cc four-stroke motor scooter
* Two different ring expressways in Japan that are numbered C3:
** Tokyo Gaikan Expressway in Tokyo, Saitama and Chiba Prefectures
** Tōkai-Kanjō Expressway in Aichi, Gifu and Mie Prefectures

## Music

* Hammond C3 organ
* High C in music (c3 in European notation)
* Low C in music (C3 in American notation)
* Tha Carter III, the title of an album by rapper Lil Wayne
* C3 Presents, independent American concert promoters

## Other uses

* C3 (classification), a para-cycling classification
* C-3 (TV channel), a children's channel on the QUBE cable system that later became Nickelodeon
* C$^3$ (light novel), a 2011 Japanese light novel series and anime by Hazuki Minase
* C3, a New Zealand logistics company owned by Linx Cargo Care Group
* C3, the code for permission to use specific land or premises for dwellings in town and country planning in the United Kingdom
* C3, the UEFA Europa League in football
* C3, a standard paper size defined in ISO 216
* Tippmann C-3, a pump-action paintball marker that uses propane gas
* C3 Church Global, a worldwide Pentecostal denomination
* C3, a class in FM radio broadcasting in North America
* Argus C3, a 35mm rangefinder camera
* Nokia C3 (disambiguation), various Nokia cellphones
* Caldwell 3 (NGC 4236), a barred spiral galaxy in Draco
* C3 policing, a methodology being employed by police to combat gangs in Springfield, Massachusetts
* Nielsen ratings that include recorded programs watched three days later
* Championing Community Children, a Philippine charitable organization abbreviated as C3
* Charles Keating III (born 1955), American former swimmer and real estate executive
* Charles III (born 1948), King of the United Kingdom and 14 other Commonwealth realms since 2022.
* C-III Capital Partners, an asset management and commercial real estate services company
* Hexadecimal number C3 (decimal 195)