A narrative song that has a theme which is transmitted aurally down through the ages.
When I visited the Field Museum in Chicago, I saw an early 15th century Chinese depiction of a sailor who asked questions of a young maiden to determine her loyalty to him. She didn't recognize him. A bulb went off. This is the "John Reilly" ballad.

These themes pop up again and again in ballads. Often the story is changed slightly
but the theme remains in tact.

The ballad Mary Hamilton goes back to Russia centuries before Joan Baez sang it.

My wife is named Mary Hamilton but as she states so often, "I don't lose my head
over it".

Frank Hamilton