intron

An intervening section of DNA occuring almost exclusively within a eukaryotic gene but which is not translated to amino acid sequences in the gene product. The introns are removed from the premature mRNA through a process called splicing to form an active mRNA.
Source:
PAC, 1992, 64, 143 (Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)) on page 158