The right answer is mostly amino acid, it can also be a start codon (which is methionin), or a stop codon, which does not code for any amino acid.
The translation of the messenger RNA is in the 5 'to 3' direction and starts at a fixed point (initiation codon: AUG), each codon encountered is "decoded" into amino acid. Each codon means a single amino acid. There is no overlap, it means that a base belongs to only one codon and therefore is only read once. Of the 64 existing codons, 3 are non-significant and correspond, with some exceptions, to end-of-translation signals (these are the STOP codons: UAA, UAG, UGA).
Thus 61 codons remain for 20 amino acids, which implies that an amino acid can be signified by more than one codon.
