'cover', as a word, is very like 'folk'....it is a short, handy term that people grab onto, no matter what the original usage, and expand the definition of so they don't have to explain themselves with a longer phrase of find a new, more precise term.

When they use it in an article, you can usually figure out in context sorta what they mean, but there is, as in this case, almost always some ambiguity that allows the discussion above. "Does cover mean 'a new version', 'a close approximation of the original', 'only a version with lyrics', 'only a version of a song by a famous singer'...?" etc...etc...

[does 'folk' mean 'old', 'anonymous'...or just something not sung by horses ;>) ]

   People simple make little attempt to use the power of the language, which, with a little effort, can be as precise as is needed.

   There's no way a simple term like 'folk' or 'cover' could survive as a precise usage...it's just too easy to distort and dilute.

Still, I guess that we end up getting a lot of information as responders answer the question with all possible definitions of the word....*wry grin*.