Prime is the lending rate banks use as a benchmark for variable-rate loans — bonds (home loans), vehicle finance, personal loans, and overdrafts are typically quoted as "prime + X%" where X depends on your credit profile. Since 1998, prime has by convention been the SARB repo rate plus 3.5 percentage points.
Prime moves whenever the SARB Monetary Policy Committee changes the repo rate. The MPC meets six times a year — every prime move is news because it directly changes monthly bond and vehicle-finance instalments for millions of households. A 0.25% rate change on a R1m bond over 20 years moves the instalment by roughly R175 a month.
Fixed-rate loans break the link — your rate is locked at the prime + margin you signed at, regardless of subsequent prime moves. Most SA bonds and vehicle finance are variable-rate by default; fixing usually costs a 1–2 percentage-point premium and is a bet on rates rising.