Chromatic: Chromatic refers to using all twelve pitches within an octave, including both the natural notes and their sharps/flats. Unlike diatonic, chromatic allows for more freedom by incorporating all possible pitches.
Non-chord tones: Non-chord tones are melodic or harmonic tones that do not belong to the underlying chord at a given moment. They add tension and interest to music by temporarily deviating from the diatonic harmony.
Key Signature: A key signature is a set of sharps or flats placed at the beginning of each staff line indicating which notes are altered throughout a piece. It helps establish the tonal center (key) of a composition.