• C-6 Canal a canal that flows from Lake Okeechobee in Florida to its terminus at the Miami River
• C-6 (explosive), a type of military explosive which is approximately 1.4 as powerful as C-4
• C6 Night Work of Young Persons (Industry) Convention, 1919
• C-6 road, a road in Metro Manilla, Philippines
• C6 tuning, the most common tuning for electric steel guitar
• AEG C.VI, a German World War I reconnaissance aircraft
• Bavarian C VI, a 1899 German steam locomotive model
• Chevrolet Corvette C6, a 2005 sports car
• Cierva C.6, a 1924 Spanish autogyro
• Citroën C6, an executive car
• DFW C.VI, a 1916 German reconnaissance aircraft
• Ford C6 transmission, an automatic transmission
• HMS C6, a British Royal Navy submarine
• LVG C.VI, a 1917 German twin-seat reconnaissance aircraft
• Sauber SHS C6, a 1982 Group C prototype racing car
• USS Olympia (C-6), a United States Navy protected cruiser

and also :

• CanJet (IATA code C6)
• Cybersex, in internet slang
• FN MAG machine gun (Canadian designation)
• Soprano C
• WinChip C6, an x86 computer chip
• C6 Envelope size
• C-6 Ute, a military version of the Beechcraft King Air airplane
• C-6, United States Army designation of the Sikorsky S-38 amphibious flying boat
• C6 protein in the complement cascade system of immune proteins (native immunity)
• In human anatomy, C6 may refer to:

* Cervical vertebra 6, one of the cervical vertebrae of the vertebral column

* Cervical spinal nerve 6

• C06, Malignant neoplasm of other and unspecified parts of mouth ICD-10 code