chord
Three or more notes sounded simultaneously, forming the basis of harmony.
In Depth
A chord is built by stacking notes, most commonly in intervals of thirds. The simplest chord, a triad, has three notes: a root, a third, and a fifth. Adding a seventh creates a seventh chord, and further extensions produce ninths, elevenths, and thirteenths.
Chords come in several qualities: major (bright), minor (darker), diminished (tense), and augmented (unsettled). Understanding chord construction and progression is central to harmony. Most Western popular music uses a relatively small vocabulary of chords, while jazz and classical music explore more complex harmonic territory.
The opening chord of A Hard Day's Night by The Beatles has been analysed by mathematicians, musicologists, and audio engineers for decades — the exact combination of notes remains debated.