Page "Exon" Paragraph 1

Portions of a precursor RNA ( introns ) may be removed by cis-splicing or by having two or more precursor RNA molecules have ligated by trans-splicing.

The mature RNA molecule can be a messenger RNA or a functional form of a non-coding RNA such as rRNA or tRNA.

Depending on the context, exon can refer to the sequence in the DNA or its RNA transcript.