A discount rate is an economic value with the unit percent that refers to the interest rate used in discounted cash flow (DCF) analysis to determine the present value of future cash flows.
Inflation rate is an economic value reprensenting the ratio between the monetary price for a good at two different points in time that equalises differences in monetary price levels between these two points in time.
Purchasing power parity is an economic value representing the ratio between currencies that equalises differences in monetary price levels between countries for the same set of goods.