Slippage refers to the difference between the expected price of a trade and the actual price at which the trade is executed. It can occur in fast-moving markets or when there is a lack of liquidity, and it can result in a trader paying more or receiving less than they had anticipated. Slippage can be positive or negative, depending on whether the actual price is better or worse than the expected price. It is an important consideration for traders, especially those who use automated trading systems or trade large volumes.