The term 'Principal Part' is used to describe the main components of a musical composition. The BODY of a musical composition is the main part, which is usually made up of chords and melodies. The LEAD is the main MELODY that is heard throughout the piece. The MELODY is the tune that is played by the instruments or sung by the vocalist. Finally, the GIST is the overall idea or theme of the piece. All of these components together make up the principal part of a musical composition.