A segment of DNA (a chemical substance that contains genetic information and is found in all living cells and some viruses) which can independently duplicate itself and insert that copy into a new position within the same or another chromosome or plasmid (unit of DNA that replicates within a cell independently of the chromosomal DNA): Transposons are similar to viruses and in humans are a cause of hemophilia, certain cancers, and other diseases.

In other organisms, transposons can become a permanent and even beneficial part of the genome, as in maize (corn), where transposons account for half of the genome, and in certain bacteria, where genes for antibiotic resistance can spread by means of transposons.

Another explanation states that a transposon is a segment of DNA that is capable of inserting copies of itself into other DNA sections within the same cell.