Modal music is music that is based on musical modes, which are types of scales other than the standard major and minor scales. Each mode has a distinct pattern of whole and half steps, giving it a unique character or "flavor." Common modes include Dorian, Phrygian, Lydian, Mixolydian, Aeolian (natural minor), and Ionian (major).
Modal music is prevalent in many genres, from ancient folk songs and medieval chant to jazz and contemporary film scores. For example, the jazz standard "So What" by Miles Davis famously uses the Dorian mode, giving it a cool, somewhat melancholic feel. Many traditional Irish and Scottish folk tunes also employ various modes.
Modes were the primary basis for Western music from ancient Greece through the Medieval and Renaissance periods, particularly in Gregorian chant. With the rise of the Baroque era, the major and minor key system (tonality) gradually became dominant. However, modes experienced a revival in the late 19th and 20th centuries, as composers sought new sounds and influences, leading to their widespread use in jazz, folk, and classical music.
Listen to the opening of Miles Davis's "So What" from his album "Kind of Blue." Pay attention to the distinct, somewhat floating quality of the melody and harmony. This piece is a prime example of modal jazz, primarily using the D Dorian mode, which gives it a different feel than a typical major or minor key piece.