A seventh chord is a type of chord that consists of four notes: the root, third, fifth, and seventh. It adds depth and complexity to music by introducing an additional note compared to a standard triad, which has only three notes. Seventh chords can create a richer sound and are commonly used in various music genres, including jazz, blues, and classical. There are several types of seventh chords, including major, minor, dominant, and diminished. Each type has a unique sound and function within a musical context. For example, a dominant seventh chord is often used to create tension that resolves to a tonic chord, making it a crucial element in harmonic progressions.