Also known as trinucleotides. A codon is made up of three nucleotides found in DNA or mRNA, and codes for one specific amino acid. The order of these three nucleotides is unique and vitally important in the coding of its amino acid.
An amino acid can be back-translated from a codon sequence by using the codon wheel.
In some instances, there can be more than one codon which corresponds to the same amino acid. 
- ↑ ALBERTS, B. et al. (2008) Molecular Biology Of The Cell. 5th edition. New York: Garland Science.
- ↑ Genetic Code Supports Targeted Insertion of Two Amino Acids by One Codon Anton A. Turanov, Alexey V. Lobanov, Dmitri E. Fomenko, Hilary G. Morrison, Mitchell L. Sogin, Lawrence A. Klobutcher, Dolph L. Hatfield, and Vadim N. Gladyshev (9 January 2009) Science 323 (5911), 259. [DOI: 10.1126/science.1164748] One codon can code for two different amino acids within the same gene, with the choice determined by an RNA structure in an untranslated region.