Q.

I think we agree on the following: in its most general sense a broadside is any single-sheet printed publication at all.

I further argue that in its more specific bibliographic sense, it is printed on one side only. This more specific sense, I believe, was the original meaning of the word.

The rest of our disagreement was about the classification of songs, not the meaning of "broadside" itself. I stand by everything I said in that area.

In particular, to folklorists, a ballad is a narrative folksong. Again, Leslie Shepard's book The Broadside Ballad is a good guide. Page 33: "It has been well said that a ballad is a song that tells a story." This is, to a certain extent, a technical term in folklore study. But it is very widely used, in Britain as well as the US, and in the folk revival as well as in scholarship. If you look, for example, at David Atkinson's recent scholarly book, or any of the folksong scholarship devoted to "ballads," or at folk albums that identify themselves as "ballads," they are almost always using this definition of a narrative folksong. (interesting exception: Pete Seeger, whose American Favorite Ballads albums featured all kinds of folksongs.) If you call any folksong at all a ballad, then you are the one using an unusual definition.

By the way, the dictionary is not always a useful guide. Within the folk music world, words often have specialized meanings, as in the case of "ballad." If someone were to ask "what's a come-all-ye," or "what's a play-party song," the OED would not help you. But someone who knows folk songs would be able to answer fairly quickly.