Slippage occurs when the price of a trade changes between the time you make the trade and the time it gets executed. In other words, the price of the transaction is different from what it was listed at the time the trade was made. This can be due to the length of time or other factors. Slippage is not unique to the Forex market and occurs in all financial markets. The reasons for it range from poor execution or high liquidity. Slippage can be quite common during economic news events or when liquidity is low, causing the spread of the price itself to spike.