Madrigal n. : A little amorous poem, sometimes called a pastoral poem, containing some tender and delicate, though simple, thought.

Madrigal n. : An unaccompanied polyphonic song, in four, five, or more parts, set to secular words, but full of counterpoint and imitation, and adhering to the old church modes. Unlike the freer glee, it is best sung with several voices on a part. See Glee.

Example:
What is the difference between a Madrigal and a Poem?

Taxonomy
madrigals, composers, music, Italian madrigals, 16th century, English Madrigals, Italy, Grove, madrigal composers, voices, The Oxford Book of English Madrigals, composition, English madrigal school, secular music, aria, instruments, 17th century, Italian.

Defination from the web:
madrigal is a type of secular vocal music composition, written during the Renaissance and early Baroque eras. ... The madrigal originated in part from the frottola, in part from the resurgence in interest in vernacular Italian poetry, and also from the ...