Slippage is an execution effect designed into how markets work: the difference between the price you requested and the price you actually received, caused by price movement between order and fill.

Slippage is usually negligible in liquid sessions and severe around high-impact news, where it can fill a stop-loss far beyond its level — turning a planned $500 loss into an unplanned $900 one that consumes daily limit you never allocated. This is the mechanical reason many programs restrict news trading, and the practical reason professional risk plans size positions assuming worst-case fills, not chart prices. Evaluate any program’s execution quality by its published slippage policy, not its marketing.