This is not my area of expertise ... but .... if Work in FRBR doesn't mean
any particular manifestation, expression or item ... what does it mean?

Do Works live in Plato's world of Ideas where abstracted version of things
exist in a more real and more true sense than any shifty mimes in our world
of sensation and change?

Is it a bit like copyright law -- Works (ideas) can't be copyrighted but
manifestations, expressions and items can?

Or is Work actually an empty container that doesn't really exist -- even in
the World of Ideas hovering over the Earth -- until it is filled with at
least one (manifestation, expression, item)?

And if so, who chose this particular word?

Was something wrong with calling it ... Idea?  Or even ... Thing?

Why work?  Work to me in plain English and even librarianese definitely
implies a manifested thing, not the idea of thing that transcends any
particular and specific expression.