A chor progression (also chord sequence and harmonic progression or sequence), as its name implies, is a series of chords played in order. Chord progressions are central to most modern European-influenced music and the principal study of harmony. Compare to a simultaneity succession. A chord change is a movement from one chord to another and may be thought of as either the most basic chord progression or as a portion of longer chord progressions which involve more than two chords (see shift of level).