What is "pastoral poem"

Madrigal \Mad"ri*gal\ (m[a^]d"r[i^]*gal), n. [It. madrigale, OIt. madriale, mandriale (cf. LL. matriale); of uncertain origin, possibly fr. It mandra flock, L. mandra stall, herd of cattle, Gr. ma`ndra fold, stable; hence, madrigal, originally, a pastoral song.]

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

   Whose artful strains have oft delayed The huddling brook to hear his madrigal.
   --Milton.

2. (Mus.) 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.