The phrase "main melody" refers to the most important or prominent musical theme in a piece of music. It is the part that stands out and is often catchy and memorable. Full definition
James Little's paintings, with their use of geometry, color, flatness and tension summon jazz music apparitions — haunting main melodies, active counter melodies, ascending offbeats and pulsing rhythms. (artzine.com)
Outside of the score, the movie goes through the effort of ending on an original song, which adds lyrics to the main melody as song by Syreeta Wright. (bloody-disgusting.com)
Even his main melody for Elisa (Sally Hawkins), which bobs on top of two undulating chords, has «the shape of water.» (latimes.com)