C2 or a derivative (C-2, C2, etc.) may refer to: Mathematics and physics C2, one of the common notations for the cyclic group of order 2 C2 differentiability class c2 the square of the speed of light (in the mass–energy equivalence formula) Biology C2 domain, a protein structural domain C2 regulatory sequence for the insulin gene Apolipoprotein C2, a human apolipoprotein In human anatomy, C2 may refer to: Cervical vertebra 2, the axis, one of the cervical vertebrae of the vertebral column Cervical spinal nerve 2 Chlorophyll c2, a form of chlorophyll Complement component 2 Procyanidin C2, a plant phenolic compound Prodelphinidin C2, a plant phenolic compound Vitamin C2, a name sometimes used for Choline the ATC code for Antihypertensives, a subgroup of the Anatomical Therapeutic Chemical Classification System C2 fragments, one of the types of products of catabolism pathways Haplogroup C-M217, also known as C2, a Human Y-chromosome DNA haplogroup Chemistry C2, Diatomic carbon, a molecule made of two carbon atoms C2=, ethylene, a two carbon alkene Codes or abbreviations C2 may be a code or abbreviation for: C2 Aquarii, a star C2 Centauri, a star C2 (Code Geass), an anime character C2 explosive, a form of plastic explosive C2 pylon, a type of high voltage pylon C2 radio class, a class in FM broadcasting in America C2 (classification), a para-cycling classification Group C2, the secondary class of Group C sports car racing BRDC C2 Championship, a short lived sports car racing series which ran from 1988 to 1990 Nimrod NRA/C2, a 1982 Group C racing car C2, an international standard paper size defined in ISO 216 (458×648 mm) C2, a level in the Common European Framework of Reference for Languages C2, the NRS social grade between C1 and D Command and control, the exercise of authority by a commanding officer over military forces in the accomplishment of a mission Air Luxor IATA airline code C2 Pictures, a film company related to Carolco Pictures Bill C-2, various legislation of the Parliament of Canada C2, or C2 a note-octave in music, aka Low C Computing C2, a computer security class, defined in the Trusted Computer System Evaluation Criteria C2, a bytecode compiler that is part of the HotSpot virtual machine implementation C2 (protocol), a 1985 Commodore file transfer protocol C2 error, a read error of a compact disc C2.com or WikiWikiWeb, the first user-editable website Cryptomeria cipher, a cipher used