An intron refers to any nucleotide sequence within a gene which is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Introns are found in the genes of most organisms and many viruses.

An exon can be referred to a sequence in DNA or its RNA transcript. In broad sense. An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule.