What is the significance of the term "diatonic" in music theory and how does it influence the overall harmonic structure of a musical composition?

The term "diatonic" in Music Theory refers to a set of seven notes within a specific key. These notes create the foundation for a composition's harmony and melody. By using diatonic notes, composers establish a sense of tonal center and create a cohesive and pleasing sound. This adherence to diatonicism helps shape the overall harmonic structure of a musical piece, providing a framework for chord progressions and melodic development.