The difference between the predicted and observed price of trading activity is called slippage. Whenever users buy and sell bitcoins, this is a common occurrence.
Slippage occurs when the implementation price of a trade differs from the desired price. Market orders cannot be met at chosen pricing when there is incredible volatility and quick markets susceptible to abrupt swings in particular trends unanticipated.

Slippage can be defined as any difference between the actual and anticipated prices. It depends on whether the trade is for buying or selling, whether the trade is for initiating or closing a trade, and the direction of price action as to whether slippage is zero, positive, or negative. Slippage can occur whenever a large market order is executing it, although there is enough movement at the designated pricing to sustain the bid/ask spread.