1. The equality of the prices of a bundle of goods (usually the CPI) in two countries when valued at the prevailing exchange rate. Called absolute PPP. 2. The equality of the rates of change over time in the prices of a bundle of goods in two countries when valued at the prevailing exchange rate. Called relative PPP. Implies that the rate of depreciation of a currency must equal the difference between its inflation rate and the inflation rate in the currency to which it is being compared.