...means Piece of Music. This field is helpful when you know the name of the song already in its Kanji/Kana form.
...is a field where you can insert a person's name that worked on the song of your choice. It can be a lyricist, an arranger, the performing band, the singer/songstress aso. Use this field when you don't know the song's name nor the Anime it belongs to, but the Performer.