chord

A chord in music is a harmonic unit formed by the simultaneous sounding of two or more notes, typically three or more distinct pitches. Most chords are built by stacking thirds above a root note to form triads—major, minor, diminished, and augmented—and can be extended with sevenths, ninths, elevenths, and thirteenths. Chords can be voiced in various inversions and textures, from compact blocks to arpeggios. In tonal harmony they function in progressions, with roles such as tonic, subdominant, and dominant that guide melodic motion.

Chords are usually notated by symbols that indicate pitch class and quality, such as C, Am7, or G7. In chord symbols, inversions are shown by specifying a different bass note (for example, C/E). Voicing, spacing, and rhythm influence color and texture though not the basic pitch content.

In geometry, a chord is a straight line segment whose endpoints lie on a curve, most commonly a circle. The length L of a circle chord at distance d from the center of a circle with radius R satisfies L = 2 sqrt(R^2 − d^2); equivalently L = 2R sin(theta/2) for a central angle theta. A diameter is a chord that passes through the center.

The word chord derives from the Latin chorda, meaning "string."