mRNA

When DNA is first transcribed into RNA, the primary transcript includes both exons and introns. Before moving out of the nucleus into the cytoplasm, the RNA goes through a splicing process that removes the introns and splices the exons together, forming the mature mRNA that will be used for the translation process into the final protein.

The coding region (also called coding sequence, or CDS), is the portion of the mRNA that is actually translated into protein. The mRNA also includes an untranslated region on each end, called the 5' UTR and 3' UTR.

Sources:  image by Robert Yates

More:  Exons can be spliced together in different combinations, in a process called alternative splicing. The next slide provides an example.