It is a trinucleotide sequence that is located at one end of tRNA (transfer RNA), which is complementary to the codon present in the mRNA sequence. Examples of anticodon:
The codon CGA on mRNA sequence codes for amino acid cysteine, tRNA corresponding to this codon is UCU anticodon.
The codon GCU on mRNA sequence codes for the alanine amino acid, and anticodon tRNA to this codon is CGA anticodon.