harmonic intervals (音程): two notes played together.
chords(和弦): three or more notes played together.
scale(音阶): a set of musical notes ordered by fundamental frequency or pitch. Due to the principle of octave equivalence, scales are generally considered to span a single octave,
pentascale（五声音阶）: five notes scale.
triad(三和弦): three-note chords.
broken chords(分解和弦): A chord broken into a sequence of notes.
arpeggios(琶音和弦): A special type of broken chords in which the notes that compose a chord are played in a rising or descending order.
Suspension triads(不和谐三和弦):比如 C-D-G or C-F-G.
Harmonic triads(和谐三和弦):比如 C-E-G.
Major Scale(大调音阶): A Major scale is made of 7 notes, and the eights duplicates the first at double its frequency so that it is called a higher octave of the same note. The sequence of intervals between the notes of a major scale is: whole, whole, half, whole, whole, whole, half
Minor Scale(小调音阶): This usually means natural minor scale. The intervals between the notes of a natural minor scale follow the sequence below: whole, half, whole, whole, half, whole, whole.
Related Scales( 关系音阶)：The two scales use the same notes but with different root, like C major and A Minor, they both use (A, B, C, D, E, F, G), but the root of C Major is C, and root of A minor is A. From the sharps and flats on scores we can NOT tell which scale it is, but observing the root is usually easily tell.
The perfect fifth (纯五度): In music theory, a perfect fifth is the musical interval corresponding to a pair of pitches with a frequency ratio of 3:2, or very nearly so. A perfect fifth interval contains 7 half steps. For example, C-G
The perfect fourth(纯四度)：In music theory, a perfect fourth is the musical interval corresponding to a pair of pitches with a frequency ratio of 4:3, or very nearly so. A perfect fourth interval contains 5 half steps. For example, C-F。
Tonic(主音), also called keynote, in music, the first note (degree) of any diatonic (e.g., major or minor) scale. It is the most important degree of the scale, serving as the focus for both melody and harmony.