The coding region of a gene, also known as the coding sequence or CDS (from coding DNA sequence), is that portion of a gene's DNA or RNA, composed of exons, that codes for protein. The region is bounded nearer the 5' end by a start codon and nearer the 3' end with a stop codon. The coding region in mRNA is bounded by the five prime untranslated region (5'-UTR) and the three prime untranslated region (3'-UTR), which are also parts of the exons.
The CDS is that portion of an mRNA transcript that is translated by a ribosome.
The coding region of an organism is the sum total of the organism's genome that is composed of gene coding regions.