Slippage is an unpleasant word for an unpleasant event. It’s the experience of not getting filled at (or even very close to…) your expected price when you place a market order. This can happen because either: market price is simply moving too fast, the market is not liquid or you’re talking to an unmotivated broker. Or, of course, all three. In spread betting this can occur if the market closes just short of your stop level and then opens up the next day a long way through you will be stopped out at the level that the market opens up at the next day and not at your stop level.