In Arab music a wazn (plural, awzān) is a rhythmic pattern or cycle, literally translated as "measure" (also called darb, mizan, and usul). (Touma 1996, p.210)

Awzan are only used in musical genres with a fixed rhythmic-temporal organization including reoccurring measures, motifs, and meter or pulse. (ibid, p.47)

A wazn consists of two or more regularly reoccurring time segments, each time segment consisting of at least two beats (naqarāt, plural of naqrah). There are approximately one hundred different cycles used in the repetoire of Arab music, most shared with Turkish music. They are recorded and remembered through onomatopeotic syllables and the written symbols O and I. (ibid, p.48)

For example, wazn wahdah sayirah (4/4), a relatively short wazn of four beats (p.50):

Wazn may be as large as 176 units of time. (p.48)

Wazn are performed on the goblet drum (tarabuka), frame drum (riqq or tar), and kettle drums (naqqarat ). (ibid, p.49)

Source

• Habib Hassan Touma (1996). The Music fo the Arabs, trans. Laurie Schwartz. Portland, Oregon: Amadeus Press. ISBN 0931340888.