When a single amino acid is encoded by more than one codon.
Explanation:
Degeneracy is when a single amino acid is encoded by more than one codon. This pehonomenon was first described by Lagerkvist where there are more codons than amino acids that could be encoded.
A mutation is a random change to genetic material. ... If a mutation occurs in a gene that results in a change to the sequence of DNA bases, then the structure of the protein that is made may also be altered. This could alter an individual's phenotype