What is "dastgah"

n. One of the basic melody types in traditional Persian music, each consisting of seven base notes and seven further variable notes used for ornamentation and modulation.

Dastgāh is a musical modal system in traditional Persian art music. Persian art music consists of twelve principal musical modal systems or dastgāhs; in spite of 50 or more extant dastgāhs, theorists generally refer to a set of twelve principal ones. A dastgāh is a melody type on the basis of which a performer produces extemporised pieces.