The muwashshah or muwaššaḥ in Arabic: موشّح, literally "girdled") can be traced back at least to the 9th century. An ornamental belt, the wišaḥ was embroidered in alternate colours interpreted formally as the "answering quality"within the stanzas and refrains of the poem (similar to an ode). But is sometimes also interpreted as the single rhyme running through each burden, like pearls hung from the belt.
This is made clearer if we consider the technical bit: the muwashshah consists of 5 stanzas (bait) of four to six lines, alternating with five or six refrains (qufl); each refrain has the same rhyme and metre (this may vary unlike classical Arabic form which uses one rhyme),but each stanza has the same metre. The kharja (final in Arabic) appears at the end of the muwashshah and often seems to have been composed independently; it is often in colloquial Arabic. (Another form often associated with the muwashshah is the zajal developed at the same time in Andalucia but, like the concluding kharja, using colloquial Arabic dialect and the local Romance dialects.)
It can also refer to a secular musical genre using muwaššaḥ texts as lyrics.
btw some define muwashshah as strophic, the strophe is a feature of the ode in classical Greek poetry and this is why you will see muwashshah often defined loosely as an ode.
More information can be found here http://en.wikipedia.org/wiki/Muwashshah