Radif is the model repertoire with modal, rhythmic and melodic potentialities anticipated for the Persian classical music.
As a matter of fact, the repertoire, while being extremely flexible, is used as a model for improvisation and composition . Almost all genres of Persian music are found in radif, including reng, chaharmezrab and tasnif , as well as rhythmic and melodic patterns.
More importantly radif contains all musical modes of Persian music, classified in larger units known as dastgahs and avaz. There are two types of radif: instrumental and vocal, with the former much longer than the letter.
Radif is by no means a unique repertoire. Expert musicians of late Qajar and early Pahlavi period (1925-1979) performed their own versions of radif. However, all versions are similar in general aspects, differing only in details. Instrumental radifs of Mirza Abdollah and Aqa Hoseyn-Qoli, and vocal radifs Mahmud Karimi and Abdollah Davami are the most important.
There are also other instrumental radifs like those by Neydavud, Shahnazi, Yusef Froutan and Sa'id Hormozi.
Nowadays, most radif versions, specially the reference ones, are transcribed.
Source: An Introduction to Iraninan music booklet from Mahoor Institute of Culture and Art