Open Dominant 7th Chords

Dominant 7th Chords (or just Open 7th Chords) can be substituted for major chords are thought of as being 'bluesy' and are often used in blues and jazz music.

Dominant 7th Chords tend to add more tension and dissonance to a chord progression than a major chord. They are often used to create a sense of movement and to create a sense of resolution to the tonic chord.