The greatest part of the world’s music is nonharmonic. Many musical styles consist basically of unharmonized melodic lines and their rhythmic organization. Harmony in the Western sense is a comparatively recent invention.
Harmony, in music, is the sound of two or more notes heard simultaneously.
Melody and rhythm can exist without harmony.
Chords are three or more single pitches that are heard simultaneously.
In music, a triad is a set of three notes that can be stacked vertically in thirds. Triads are the most common chords in Western music.