A classic rate cryptocurrency exchange is an exchange performed at the current most profitable rate on the market.
An expected rate is the current exchange rate you will get. However, the cryptocurrency market is highly volatile and you should account for that.
During the classic rate exchange, each transaction may have its own unique exchange rate because of price fluctuations, market conditions, and network fees. The rate might change at any moment; as a result, you might receive more or less than you thought you would.