Melody is the underlying structure of a musical composition that carries the main theme or idea. It is the series of notes that are played sequentially to create a memorable and cohesive musical passage. Melodies can be simple or complex, and they are typically the most recognizable and memorable aspect of a song.

Harmony, on the other hand, refers to the combination of different notes played simultaneously to support and complement the melody. It adds depth and richness to the overall sound of a piece of music. Harmony can create tension or resolution, and it plays a crucial role in creating the emotional impact of a song.