What is the significance of the tonic in music theory and how does it relate to the overall structure of a musical composition?

The tonic is the main or home note in a musical key, providing a sense of stability and resolution. It serves as a central point around which other notes and chords revolve, creating a sense of tension and release in a composition. The tonic helps establish the key of a piece and influences the overall structure by providing a point of reference for the listener to understand the harmonic progression and form of the music.