A dominant is the fifth grade or tone in any major or minor scale. It is so called because it is second in importance only to the first tone of its key, which is called the tonic. When the seventh degree is added to the triad which is constructed on the dominant (the fifth degree), we have a "seventh" chord which leads strongly to the tonic and is accompanied by a feeling of resolution.
In harmony, the dominant chord is usually represented by the Roman numeral V.
