Covered interest rate parity is an arbitrage relation that states that forward exchange rates are a function of current spot rates and interest rates in each currency. Essentially it says that you can’t profit by borrowing in one currency and investing in another over a period because the forward rate you would lock in would exactly offset the changes in value due to the different interest rates. It is an arbitrage reltiaon because you know all factors at the present time, you know the current spot rat, you know the interest rates for each currency and you can lock in a price with the current forward rate.
Uncovered interest rate parity has nothing to do with forward rates, it is forecasting EXPECTED FUTURE SPOT RATES. It states that the expected future spot rate is a function of the current spot rate and the interest rates of each currency. It is not an arbitrage relation because you cannot lock in the future spot rate at the present time.
You’ll notice that they are pretty much the same thing, and if the forward rate is an unbiased predictor of the future spot rate then they are the same thing. The critical difference is that covered parity uses forward rates you can lock in TODAY and uncovered forecasts the spot rate that will occur at time T.