Exon

The exon is the region of a gene that contains the code for producing the gene's protein. Each exon codes for a specific portion of the complete protein. In some species (including humans), a gene's exons are separated by long regions of DNA (called introns or sometimes "junk DNA") that have no apparent function. A gene that consists of a string of exons can create several gene products or proteins by alternative splicing.

Sources

http://www.genome.gov/glossary.cfm?key=exon