Enhancer

In genetics, an enhancer is a short region of DNA which can be bound with proteins (namely, the trans-acting factors, much like a set of transcription factors) to enhance transcription levels of nearby genes (hence the name) in a gene-cluster.

It does not need to bind close to the transcription initiation site to affect its transcription, as some have been found to bind several hundreds of thousands base pairs upstream of the start site. They can also be found downstream of the gene, or inside introns.