Tonality

Modal

music based on modes rather than major or minor scales

Atonal

music that lacks a key center

Bitonal

music written in two different keys played simultaneously

Polytonal

music involving more than two keys played simultaneously

Tonic

the first note of a scale or key

Dominant

the fifth note of a scale

Relative minor

the minor key sharing the same key signature as a major key

Modulation

the process of changing from one key to another within a piece

Tonicisation

temporarily emphasizing a new tonic within a key

Transposition

shifting a piece of music to a different key or pitch