What is "carbon-13"

n. (context isotope English) the least abundant of the two stable isotopes of carbon, (nuclide 13 6 C), having six protons and seven neutrons

Carbon-13 (C) is a natural, stable isotope of carbon with a nucleus containing 6 protons and 7 neutrons. One of the environmental isotopes, it makes up about 1.1% of all natural carbon on Earth.