The sequence of three nitrogen bases present on the m-RNA which specifies a single amino acid is called a Codon.
e.g. The codon GCU specifies the amino acid Alanine.
The sequence of three unpaired nitrogen bases present on the middle loop of t-RNA which is complementary to a specific codon of m-RNA is called anticodon.
e.g. The t-RNA for Alanine has the anticodon CGA.