folk song vs poem

folk song

noun
  • folk music 

  • A song, in any folk style, originating among ordinary people, usually non-professional musicians, and handed down by oral tradition. 

  • A song in the style of folk music, a modern genre of popular music. 

poem

noun
  • A piece of writing in the tradition of poetry, an instance of poetry. 

  • A piece of poetic writing, that is with an intensity or depth of expression or inspiration greater than is usual in prose. 

  • A literary piece written in verse. 

How often have the words folk song and poem occurred in a corpus of books? (source: Google Ngram Viewer )