Harmony in music refers to the concept of combining different sounds together to create new, distinct musical ideas. It is one of the three main elements of music, along with melody and rhythm. Harmony involves the juxtaposition of individual pitches to create chords, and in turn, the juxtaposition of chords to create larger chord progressions. The principles of connection that govern these structures have been the subject of centuries worth of theoretical work.
Harmony can be understood to involve both a "vertical" dimension (frequency-space) and a "horizontal" dimension (time-space), and often overlaps with related musical concepts such as melody, timbre, and form. In a narrower sense, harmony refers to the extensively developed system of chords and the rules that allow or forbid relations between chords that characterizes Western music.
Harmony is what occurs when more than one note is played or sung at the same time, either as an interval (two notes) or chords of three or more notes. It deals with the ‘vertical’ aspects of music, whereas melody and rhythm deal with ‘horizontal’ aspects. The interaction of two or more musical notes that sound at the same time is called harmony.
