1. Codons which do not code for an amino acid. They signal ribosomes to terminate protein synthesis. The codons are UAA, UAG and UGA, and have been termed ochre, amber and opal, respectively. Also known as stop codons or termination codons. Often two of these codons are found together at the end of a coding sequence of RNA.

2. In the Sanger method of DNA sequencing, di-deoxynucleoside triphosphates are added as chain terminators in the synthesis of a complementary DNA strand.