Dark Fiber

A dark fibre or unlit fibre is an unused optical fibre, available for use in fiber-optic communication. The term dark fibre was originally used when referring to the potential network capacity of telecommunication infrastructure, but now also refers to the increasingly common practice of leasing fibre optic cables from a network service provider, or, generally, to the fibre installations not owned or controlled by traditional carriers. In common vernacular, dark fibre may sometimes still be called "dark" if it has been lit by a fibre lessee and not the cable's owner. https://en.wikipedia.org/wiki/Dark_fibre