A hospital cash plan pays a fixed daily amount (typically R500 to R3,000/day) for every day you're admitted, regardless of the actual treatment cost. It's regulated as insurance, not medical aid, and pays YOU directly, not the hospital. Useful as income protection while you can't work, or to help with deductibles and co-pays. Never a substitute for medical aid: a R150,000 hospital bill is not paid by R2,000/day for 5 days.
SA example: A R200/month hospital cash plan paying R2,000/day. You're admitted for 4 days, so you receive R8,000 in cash. The hospital bill itself is still paid by your medical aid.