This can be done to reduce the vessel's build cost by not purchasing the system at the time of construction, as a method of future-proofing a design, or for security purposes.
[1] The term is usually used in regard to ships but sometimes extends to military vehicles, aircraft and other hardware.
[1] Provision is made physically with power supply and data wiring to a hardpoint or through software for the installation of a weapon or system which is marked for purchase at a later date, with installation during the vehicle's modernisation or refit.
[1] Part of the justification for this design concept is the implicit assumption that in the event of the system being required (such as a war), there should be enough warning time to purchase the system, install it in the vehicle, and train operators in its use.
[2] Fitting for but not with can range anywhere between leaving sufficient space for any future upgrades, to installing a weapon system during construction but not purchasing ammunition until it is needed.