A song written down for posterity in a museum or collection is a "Text"
If you are singing it its up to you what you call it as long as you don't claim it as you own composition I suppose.
A song is only a text,an idea, or a memory unless it is being sung.
When it is being sung it is so many things that I would say it is whatever it is to the people hearing ,singing or remembering it and its associations to and for themselves.