PMBs are the legal floor of medical aid cover in South Africa. Established by the Medical Schemes Act, they're a list of 271 acute conditions and 27 chronic conditions (the CDL) that every scheme must diagnose, treat, and care for in full, regardless of which plan you're on. Schemes can require you to use Designated Service Providers (DSPs) for non-emergency PMB treatment; if you go outside the DSP voluntarily, you may owe a co-payment.
SA example: You're on KeyCare Core and you have a heart attack. The scheme must cover diagnosis, hospitalisation, surgery, and ongoing chronic medication for life, even though it's the cheapest plan.