Chord
The simultaneous sounding of at least three different notes.
What it means
A chord is the simultaneous sounding of at least three different notes. The simplest and historically most basic chord type is the triad, built from a root, a third above it, and a fifth. Adding further thirds produces four-note chords such as the seventh chord or the ninth chord.
A chord remains the same chord regardless of the order or octave in which its notes sound, as long as the pitch classes match; which note sits in the bass merely determines the inversion.
In the notation
In notation, chords are usually written as noteheads stacked on a shared stem. In figured-bass and jazz practice, chords are instead often indicated by chord symbols (e.g. C, Am7, G7) or by figures above a bass line, without spelling out the individual notes.
Musical use
Chords have formed the backbone of harmony in Western music since the polyphony of the Renaissance, and especially since major-minor tonality took shape in the 17th century. Successions of chords, known as chord progressions or cadences, create tension and resolution and structure musical form.
A chord should be distinguished from a mere interval, which consists of only two notes, and from a cluster, in which many closely spaced notes sound together without a systematic thirds-based structure. In popular music and jazz, chords are usually named through chord symbols, while classical theory more often characterizes them through scale-degree labels such as tonic, subdominant, or dominant.
Depending on their interval structure, consonant chords such as the major and minor triad are distinguished from dissonant chords such as the diminished or augmented triad, which in harmony theory usually require resolution into a consonant chord.
Performance practice
Practice chords first as pure hand shapes or fingerings before applying them within a piece: this lets you internalize the hand position without also having to track rhythm or melody. Aim to strike or press all the notes of a chord as simultaneously and evenly as possible, so the sound does not fall apart.