Enhancer (genetics)
In genetics, an enhancer is a short region of DNA that can be bound with proteins (namely, the trans-acting factors, much like a set of transcription factors) to enhance transcription levels of genes (hence the name) in a gene cluster. While enhancers are usually cis-acting, an enhancer does not need to be particularly close to the genes it acts on, and sometimes need not be located on the same chromosome.
Read more about Enhancer (genetics): Enhancer Locations, Theories, Enhancers in Developmental Biology, Enhancers and The Evolution of Developmental Mechanisms