A beit is a metrical unit

Meter (poetry)

In poetry, metre is the basic rhythmic structure of a verse or lines in verse. Many traditional verse forms prescribe a specific verse metre, or a certain set of metres alternating in a particular order. The study of metres and forms of versification is known as prosody...

 of Arabic, Iranian and Urdu poetry

Urdu poetry

Urdu poetry is a rich tradition of poetry and has many different types and forms. Borrowing much from the Persian language, it is today an important part of Pakistani and North Indian culture....

. It corresponds to a line

Line (poetry)

A line is a unit of language into which a poem or play is divided, which operates on principles which are distinct from and not necessarily coincident with grammatical structures, such as the sentence or clauses in sentences...

, though sometimes improperly renderered as "couplet

Couplet

A couplet is a pair of lines of meter in poetry. It usually consists of two lines that rhyme and have the same meter.While traditionally couplets rhyme, not all do. A poem may use white space to mark out couplets if they do not rhyme. Couplets with a meter of iambic pentameter are called heroic...

" since each beit is divided into two hemistich

Hemistich

A hemistich is a half-line of verse, followed and preceded by a caesura, that makes up a single overall prosodic or verse unit. In Classical poetry, the hemistich is generally confined to drama. In Greek tragedy, characters exchanging clipped dialogue to suggest rapidity and drama would speak in...

s of equal length, each containing two, three or four feet, or from 16 to 32 sylables.

William Alexander Clouston

William Alexander Clouston

William Alexander Clouston of Orkney was a 19th century British folklorist.A Supplement to Alliborne's Dictionary , as quoted in Folklore, gives the following biographical information:b...

 concluded that this fundamental part of Arabic prosody originated with the Bedouins or Arabs of the desert

Desert

A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...

, as, in the nomenclature of the different parts of the line, one foot is called "a tent-pole", another "tent-peg" and the two hemistich

Hemistich

A hemistich is a half-line of verse, followed and preceded by a caesura, that makes up a single overall prosodic or verse unit. In Classical poetry, the hemistich is generally confined to drama. In Greek tragedy, characters exchanging clipped dialogue to suggest rapidity and drama would speak in...

s of the verse are called after the folds or leaves of the double-door of the tent or "house".