Slippage means that the bid and the Ask spread is so volatile that the price changes between the time your market order is placed and the time it is executed. This Change can be positive and negative. It simply means that there is a difference between the execution price and the actual execution price.
Intended Execution price +/- Actual execution price= Slippage
To protect the clients XtreamForex executes every trade according to its best execution policy this means that whenever slippage occurs your trade will be always be executed at the next best available price. Most commonly the slippage will occur at the times of the low liquidity or the high volatility. This could be because of a major news event, big political or the market announcement, or simply whether the trade is market hows. Every trade involves a risk of the slippage but there are some ways you can try to limit your exposure.