what is a dominant 7th chord

A dominant seventh chord is a type of seventh chord that consists of a dominant triad (root, major third, and perfect fifth) and an added minor seventh above the root. It is usually built on the fifth degree of the major scale and is composed of a root, major third, perfect fifth, and minor seventh. For example, in the key of C major, the dominant seventh chord is G7, which consists of the notes G, B, D, and F. Dominant seventh chords are often abbreviated with a simple 7. The dominant seventh chord is perhaps the most important of the seventh chords and is found almost as often as the dominant triad in classical music. It typically functions to drive the piece strongly toward a resolution to the tonic of the key. Dominant seventh chords can also be used to modulate to another key.