I don't have my prosodic handbook at the ready, but, to the best of my recollection, the "classic" ballad structure in English is a narrative without a refrain or chorus, *usually* in iambic tetra- or pentameter (4 or 5 duh-DUHs to a line) rhyming abab or abcb.

Contemporary pop music has sort of co-opted the prosodic terminology--ballads, as John Hardly cites, have become something less technical. The same goes for anthems, in my opinion. "We will, we will, Rock You" (Queen) is not, in my opinion, an anthem, but that's how the popular music world has classified it.

Just my $0.02, fwiw.

V