Said of products or solutions that a customer, especially a government customer, can buy and use without having to pay for their development to specific customer (especially government) requirements or specifications, because those products or solutions have already been developed to government requirements or specifications. Thus when the US Navy buys combat boots, it's buying Government-off-the-shelf equipment, because the US Army has already developed them.
Products or solutions of this kind. Commonly referred to by the acronym GOTS. Compare commercial-off-the-shelf, COTS.