What's a Tetrad ?
A basic chord is built with three notes this is what we call "triad chords" or "triads". Tetrad chords aka "four note-chords" are simply chords containing four notes, “tetra“ is a Greek root meaning four. This means that tetrads are triads with an additional note which can be a major seventh (7) or a minor seventh (b7).
One of the fundamental theoretical elements to understand music is the harmonization of the major scale. Harmonizing scale is building chords with notes. This lesson explains how to create triads and seventh chords from each note of the major scale.