stop codon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of three codons, UAA, UAG, or UGA, that signal the termination of the synthesis of a protein.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biology , (genetics), (biochemistry) a sequence of three RNA nucleotides (A, C, G or U) that instruct the synthesis, or translation, of a protein to stop. The three-letter stop codon sequences have been given names: "UAG" is amber, "UGA" is opal, and "UAA" is ochre.