I use it in a way it's used in disciplines that also work with specialty-built, or even custom-built equipment. Such as science, military and some types of engineering (e.g. aerospace). The first sentence of the linked article describes it:

"Commercial off-the-shelf or commercially available off-the-shelf[1] (COTS) products are packaged solutions[buzzword] which are then adapted to satisfy the needs of the purchasing organization, rather than the commissioning of custom-made, or bespoke, solutions."

So for example, a research team may decide to not spend money on expensive scientific cameras for monitoring experiment, and instead opt to buy an expensive - but still much cheaper - DSLR sold to photographers, or strap a couple of iPhones 15 they found in the drawer (it's the future, they're all using iPhones 17, which is two generations behind the newest one). That's using COTS equipment. COTS is typically sold to less sophisticated users, but is often useful for less sophisticated needs of more sophisticated users too. But if COTS cameras start to accrue built-in algorithms that literally fake data, it may be a while before such researchers realize they're looking at photos where most of the pixels don't correspond to observable reality, in a complicated way they didn't expect.