With regard to futures contracts as well as other financial instruments, slippage is the difference between where the computer signaled the entry and exit for a trade and where actual clients, with actual money, entered and exited the market using the computer’s signals. Market impact, liquidity, and frictional costs may also contribute.

Slippage refers to the difference between the expected price of a trade and the price at which the trade is executed. Slippage can occur at any time but is most prevalent during periods of higher volatility when market orders are used. It can also occur when a large order is executed but there isn't enough volume at the chosen price to maintain the current bid/ask spread.