Without going into the details, it essentially means that the dealer has allocated R40,000 extra to deal. This is normally made up of a combination of profit and factory rebate. Bottom-line is that they can give you normal trade-in value for your car plus R40k on top.
Be advised that dealers might try to 'pad' the deal; they might offer you R10k or R15k less on the trade-in, which will still equate to R25k-R30k more than normal once the R40k has been brought into the equation. The rebate from the manufacturer is often linked to being able to supply paperwork on the vehicle traded in to them, so no trade-in no rebate.