Harmony is when more than one pitch is sounding together at the same time. Harmony like melody and rythm, is one of the basic elements of music, though might not be as important since there can never exist a concept like harmony alone. You can have music that is just rhythms, with no pitches at all. You can also have music that is just a single melody, or just a
melody with rhythm accompaniment. But as soon as there is more than one pitch sounding at a time, you have harmony.
Harmony when it comes to music is what makes music more pleasing to the ear. Harmony unites the chords and notes played together in a piece at the same time and creates a harmonius relationship. In western music harmony is most emphasized compared to the kind of music on other parts of the world which may emphasize other aspects of music like rythms foristance music of African origin