Indefeasible rights of use
Indefeasible right of use (IRU) is a type of telecommunications lease permanent contractual agreement that cannot be undone, established between the owners of a communications system and a customer of that system. The word "indefeasible" means "not capable of being annulled, or voided, or undone".
Source: Wikipedia — Indefeasible rights of use (CC BY-SA 4.0)