The E7 chord is a dominant seventh chord built on the note E. It consists of four notes: the root E, the major third G#, the perfect fifth B, and the minor seventh D. This chord is commonly used in various music genres, including blues, jazz, and rock, to create tension that resolves to the tonic chord. In music notation, the E7 chord is often represented as "E7." It can be played on various instruments, such as the guitar and piano. The unique sound of the E7 chord adds richness and complexity to musical compositions, making it a popular choice among musicians.