Dark Fiber refers to optical fiber infrastructure that has not yet been lit (*lit fiber), meaning it is installed but is not yet being used (no data transmission). 

Dark fiber is rented by broadband providers who need to control their own network, so instead of leasing a service, they lease infrastructure that allows them to build their own network with their own equipment. 

Dark fiber gives clients the capacity to increase bandwidth as needed without paying any additional monthly costs and decreases dependence on carrier response times during events and for upgrades. 

 Dark fiber is usually priced per strand per mile for a set period. The dark fiber providers often offer their client the option of an indefeasible right of use (IRU)** which can range between 20 to 30 years, paid upfront along with annual payments for maintenance.

*Lit Fiber: This term is the opposite of dark fiber and refers to a Fiber Optic cable that is active and able to transmit data. ** Indefeasible Right of Use (IRU) : A contractual agreement (temporary ownership) of a portion of the capacity of a fiber optic cable.