tonal center of a diatonic scale
In music, the tonic note is the first note in a diatonic scale. It is the tonal centre, or the tone on which the music sounds finished. The triad, or chord, based on the tonic note, is the tonic chord. All other notes in a piece of music use the tonic note as a reference point. Musical scales are named after the tonic note. For example, the tonic of a scale of C, is the note C. The tonic is always numbered as one, or in traditional music theory as I (using Roman numerals).