Diminished Seventh Chord: A diminished seventh chord refers to a four-note chord consisting of two minor thirds stacked on top of each other. It adds tension and dissonance to music.
Supertonic Chord: The supertonic chord refers to the second scale degree chord in a key. In a viio-ii progression, it is represented by the Roman numeral "ii."
Dissonance: Dissonance refers to musical intervals or chords that sound unstable or tense. It creates contrast and resolution when resolved to consonant sounds.