Definition for Enhancer
From Biology Forums Dictionary
1) A response element in eukaryotes that increases the rate of transcription.
2) Enhancers are DNA sequences that typically have binding sites for several different activators and repressors. They are located somewhere in the vicinity of the gene, much farther away than promoter sequences, sometimes tens of kilobases away. They allow complex and nuanced control of gene expression depending on a number of different conditions such as developmental stage, tissue type, and response to extracellular signals.