A chord progression (or harmonic progression) is a series of musical chords, or chord changes that "aims for a definite goal" of establishing (or contradicting) a tonality founded on a key, root or tonic chord. Chords and chord theory are generally known as harmony.
A chord progression can be thought of as a harmonic simultaneity succession: it offers an ongoing shift of level that is essential to the music of Europe (at least since 1600), Oceania and South/West Africa. A change of chord, or "chord change", generally occurs on an accented beat, so that chord progressions may contribute significantly to the rhythm, meter and musical form of a piece, delineating bars, phrases and sections. (Courtesy of Wikipedia)