A medical scheme is a registered, non-profit entity. Every member pays a monthly contribution into a shared fund, and that fund pays providers when members claim. Schemes are member-owned in the legal sense. They exist to serve members, not generate profit. They're separate from the for-profit administrators (like Discovery Health (Pty) Ltd) that run them day-to-day.
SA example: Discovery Health Medical Scheme (DHMS), Bonitas, GEMS, and Momentum Health are all medical schemes. Discovery Health (Pty) Ltd is the administrator that runs DHMS but is a separate, for-profit company.