Lyric songs.
Arguably some of these could also be classified as ballads as often they are the remnants of ballads where all that remains is a riddle section or a lament. Many versions of the 'Died for Love' family or the 'Waly Waly' family often survive only as a collection of lyric pieces with no progression.
Then again some of the ballads in Child's collection are little more than gatherings of commonplaces from other ballads.

Just to complicate matters! Stir, stir!