People define "ballad" to suit themselves. The word comes from old Provencal, balada (Late Latin ballare, to dance), a song sung while dancing. It has accumulated several meanings. The principal meaning now is a narrative composition in rhythmic verse suitable for singing.

Its primary meaning is a song intended as the accompaniment to a dance. OED. The secondary definition is "a light, simple song of any kind but it has come to mean a sentimental or romantic composition in verses." OED
Its present meaning is nebulous. Martin Ryan's comments are pertinent.