[exikyut]

Ooooooh. I thought "dark" was some weird domain-specific nomenclature to describe "not available on the open market", with the open market being like a transport network of (lit up) lines, and dark = not lit up = not on the open market.

Now I actually understand the definition I'd say "unlit fiber" feels like a better-resolved way of putting it, although I could see the uninitiated imagining that describing a service that needed an additional subscription on top or something, which isn't quite the right nuance.