A seventh chord is a type of chord that consists of four notes: the root, third, fifth, and seventh. It adds a richer sound compared to a basic triad, which only includes three notes. Seventh chords can be built on any note and are commonly used in various music genres to create tension and resolution. There are several types of seventh chords, including major, minor, dominant, and diminished. Each type has a unique sound and function in music. For example, a dominant seventh chord, often used in jazz and blues, creates a strong pull back to the tonic chord, enhancing musical progression.