Non Diatonic Chords 

There are a variety of chords in music that aren't included among the built-in diatonic chords of the major scale (1, 2m, 3m, 4, 5, 6m, and 7dim) . These chords are prominent in 6+ chord charts.

Secondary Dominants are chords like Major 2, 3, 6, or 7 chords.

Mode Mixture chords include chords like b3, 4m, 5m, b6, and b7.

Diminished and augmented chord qualities, as well as chords built off chromatic notes, are covered here.