The base sequence of three nucleotides in m-RNA that act as code words for amino acids in proteins constitute the triplet code or genetic code or codon.
The smallest sequence of nitrogen bases (nucleotides) in the m-RNA which specify one particular amino acid is called a triplet code or codon.
Each codon consists of three successive nucleotide base pairs in the m-RNA.
The m-RNA bases (A,U,C,G) serve as the four alphabets of the coded language.
For example,
The triplet code or Codon AUG codes for the amino acid Methionine
The triplet code or Codon GUA codes for the amino acid Valine.