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 (https://doi.org/10.1351/pac199264010143)