What does it mean for the 90-day forward exchange rate to be an unbiased predictor of the

Question:

What does it mean for the 90-day forward to be an unbiased predictor of the future spot Exchange Rate
The value of one currency for the purpose of conversion to another. Exchange Rate means on any day, for purposes of determining the Dollar Equivalent of any currency other than Dollars, the rate at which such currency may be exchanged into Dollars...