an enhancer is a short (50–1500 bp) region of DNA that can be bound by proteins (activators) to increase the likelihood that transcription of a particular gene will occur. These proteins are usually referred to as transcription factors. Enhancers are cis-acting. They can be located up to 1 Mbp (1,000,000 bp) away from the gene, upstream or downstream from the start site. There are hundreds of thousands of enhancers in the human genome. They are found in both prokaryotes and eukaryotes.
Ref: Enhancer (genetics) – Wikipedia
Enhancer RNAs (eRNAs) represent a class of relatively long non-coding RNA molecules (50-2000 nucleotides) transcribed from the DNA sequence of enhancer regions. They are not mRNAs. The expression of a given eRNA correlates with the activity of its corresponding enhancer in target genes. Increasing evidence suggests that eRNAs actively play a role in transcriptional regulation. Their mechanisms of action remain unclear.