Your market rate is the index plus a margin, whether that margin be a +1 or a -1. A discount, or premium, would be a rate that is calculated by a formula, or a set figure, different from the market rate. As an example if the market rate calculated at 6%, but the initial rate was 5% then you have discounted the rate by 1%.
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The opinions expressed are mine and they are not to be taken as legal advice.