Hazaj meter is a quantitative verse metric frequently found in the epic poetry of the Middle East and western Asia. A musical rhythm of the same name is based on the literary meter.
Like the other meters of the al-'arud system of Arabic poetry, the basic rhyme unit of hazaj meter compositions is a closed couplet—a bai't "distich" (literally "tent")—of two hemistichs known as misrás ("tent flaps"). When arranged in quatrains of two bai'ts, verse in hazaj meter typically has an 'aa ba' rhyme scheme; the first, second and fourth half-lines must rhyme, while the third need not and generally does not. The two bai'ts in hazaj meter then constitute a ruba'i, plural rubai'yat.
Characteristic of the hazaj meter (in relation to the other al-'arud meters) is its leading iamb, that is, the first two syllables of its prosodic feet are short-long. This syllable pair (the watad, "peg") is then repeated at fixed points along the length of a line, and two variable syllables (the sabab, "guy-wire"s) are "tied" to each instance of it. The hazaj measure is thus nominally tetrasyllabic. Its two common variations are:
The two variable syllables are subject to the substitution rules of the al-'arud system in which a long syllable is equal to two short syllables, and certain long syllables may be shortened under certain conditions. There are some five permutations—zihafat "relaxations"—predefined for the two variable syllables of the hazaj meter. Each line of a composition in the meter will have approximately the same number of syllables.
Although first codified in the al-'arud prosody system of the 8th century philologist and lexicographer Khalil ibn Ahmad, and thus formally a classical Arabic poetry meter, the hazaj meter is also represented in Hebrew-, Ottoman Turkish-, Persian and other Iranian-, Urdu- and other North Indian language epic poetry traditions.
By the 11th century, the hazaj meter had become "the most popular meter for romantic epics" in Iranian language compositions. "The preference for Hazaǰ-type meters may be explained in terms of their relationship to folk verses and songs. The meter of hazaǰ and its variations are among the ones most frequently found in folk poetry such as do-baytī and lullabies (lālā'ī). The meter of hazaǰ-e mosaddas-e maḥdūf e maqṣūr, which is the meter of do-baytī (or čār-baytī in regional dialects), is particularly often sung in the āvāz-e Daštī, which is closely associated with Iranian folk tunes."
The hazaj meter is also among the three most commonly used metrics in Urdu verse, and it is one of the typical meters of the ghazal genre. The hazaj meter is perhaps also be the base metric of contemporary Arabic band compositions, but this is uncertain. Particularly notable Persian language compositions in hazaj meter include the Rubaiyat of Omar Khayyam, Fakhr al-din Gurgani's Vis u Ramin, and – for its length of 6,150 verses – Nezami's Khusrow o Shirin.