The term reng in Persian traditional music (music from the Qajar period and thereafter) is used for a rhythmic instrumental genre performed in 6/8 beat and in a medium or fast tempo. This is a genre to which Persian dance is performed. But, before the Qajar period, when Persian music was totally depended on the radif (the classical repertory of Persian music), all the rhythmic pieces at the end of each dastgah were called reng. Because of this, the reng can be performed in different meters. Some of the radif's rengs are in 6/4 beat like the Nastari in dastgah-e nava, or in 2/4 like Harbi in dastgah-e mahur. Also, there are many rengs with 6/8 beat in the radif, such as shahr-ashub in dastgah-e shur and dastgah-e mahur.
The first appearance of the term reng as a musical term dates back to the beginning of the Safavid Period. ...