The madrigal is traditionally a polyphonic form, originally from Italy, that typically consists of a five- to fourteen-line poem composed of varying meter with seven to eleven syllables per line and the last two lines as a rhyming couplet.
From A Poet’s Glossary
The following definition of the term madrigal is reprinted from A Poet’s Glossary by Edward Hirsch.
A verse to be sung to music; a secular vocal composition for two or more voices. The madrigal originated as a pastoral song (matricale was the medieval Latin name for a country song) in northern Italy in the fourteenth century. The simple rustic song consisted of two or three three-line tercets followed by one or two rhyming couplets. The lines were either seven or eleven syllables long.
The madrigal was revived by composers throughout Europe in the sixteenth century. It was freed of its traditional formal strictures; all that remained of the original form was the final rhyming couplet, which has also been abandoned in most modern madrigals. The English madrigal especially flourished from the 1580s to the 1620s. Thomas Morley (1557–1602), Thomas Weelkes (1576–1623), and John Wilbye (1574–1638) were all great English madrigal composers. Here is one of my favorite anonymous Elizabethan madrigals:
My Love in her attire doth show her wit,
It doth so well become her;
For every season she hath dressings fit,
For Winter, Spring, and Summer.
No beauty she doth miss
When all her robes are on:
But Beauty’s self she is
When all her robes are gone.