Aeolian Mode	- The traditional mode built upon the 6th scale step; ex., the Aeolian scale mode in C major key would be a scale starting on A and conforming to the key signature of the major key relation.
Altered Note	-the 9, #9, #11,flat5, flat13 of a chord.
Cycle of Fifths	a circular distribution of key centers shown in a graphical layout. The Cycle (circle) of fifths map to the overtone system. The natural resolution of key centers follows the arc of the cyclic layout.
Dorian Mode	The traditional mode built upon the 2nd scale step; ex., the Dorian scale mode in C major key would be a scale starting on D and conforming to the key signature of the major key relation.
Enharmonic	two differently spelled notes that sound the same-same frequency. e.g., C# & Dflat.
Half diminished	a minor seventh chord with a flat fifth. Also, a chord built off the seventh mode of the major scale.
Interval	the space between two tones.
Ionian Mode	The traditional mode built upon the 1st scale step; ex., the Ionian scale mode in C major key would be a scale starting on C and conforming to the key signature of the major key relation. This is identical to the C Major scale.
Locrian Mode	The traditional mode built upon the 7th scale step; ex., the Locrian scale mode in C major key would be a scale starting on B and conforming to the key signature of the major key relation.
Lydian Mode	The traditional mode built upon the 4th scale step; ex., the Lydian scale mode in C major key would be a scale starting on F and conforming to the key signature of the major key relation.
Melodic Minor Scale	a scale featuring a minor third and major seventh-in root position. A major scale with a minor third.
Mixolydian Mode	The traditional mode built upon the 5th scale step; ex., the Mixoydian scale mode in C major key would be a scale starting on G and conforming to the key signature of the major key relation.
Phrygian Mode	The traditional mode built upon the 3rd scale step; ex., the Phrygian scale mode in C major key would be a scale starting on E and conforming to the key signature of the major key relation.
Partials	The set of many naturally occurring tones, or harmonics, produced by the vibrations of objects. In musical instruments, the relative strengths of the individual partials produced by a single note contribute to the characteristic timbre of the sound. Partials are also called overtones.
Slash Chord	a chord played over a bass note not a chord member.
Sus Chords	Chord construction where the 3rd step is replaced by a a note is sustained over a chord change.
Tetrachord	traditionally, a four note scale structure, spanning a segment of the scale as a contiguous perfect fourth interval.
Timbre	in music, the characteristic sound of an instrument, determined by the features of the inherent partials, or overtones, distribution.
Tonic	The 1st degree of the scale defined.
Tonicization	A temporary movement to a remote key center within a phrase.
Tritone	interval spanning an augmented fourth, or, three whole steps. Ex., C – F#. The tritone interval built on the tonic of the scale divides the octave in equal halves-Tritone intervals are an important consideration in the creation and resolution of Dominant Seventh chords.
Tritone Substitution	a V chord substituting for another V chord a tritone interval away. Both chords share the same 3rd and 7th which are also separated by the tritone interval.
Whole Tone Scale	a scale consisting of only whole steps.