1. A sequence found in eukaryotes and certain eukaryotic viruses which can increase transcription of a gene when located (in either orientation) up to several kilobases from the gene concerned. These sequences usually act as enhancers when on the 5´ side (upstream) of the gene in question. However, some enhancers are active when placed on the 3´ side (downstream) of the gene. In some cases enhancer elements can activate transcription of a gene with no (known) promoter.

2. A substance or object that increases a chemical activity or a physiological process.

3. A major or modifier gene that increases a physiological process.