Although 61 codons code for aminoacids, only 20  amino  acids are naturally  occurring. This feature of the genetic code is known as:
THE GENETIC CODE IS DEGENERATE, UNAMBIGUOUS, NONOVERLAPPING, WITHOUT PUNCTUATION, & UNIVERSAL
Three of the 64 possible codons do not code for specific amino acids; these have been termed nonsense codons. These nonsense codons are utilized in the cell as termination signals. They specify where the polymerization of amino acids into a protein molecule is to stop. The remaining 61 codons code for the 20 naturally occurring amino acids.
Thus, there is  “degeneracy” in the genetic code—that is, multiple codons decode the same amino acid.
Reference- Harper 30th edition Pg- 414
Transcription
Degeneracy
Mutation
Unambiguity