Definition

Slippage

The difference between where a stop is set and where it actually fills — a mechanical consequence of how stop orders work.

Full Explanation

A stop guarantees a trigger, not a price. When a stop fires, it becomes a market order that executes at whatever is currently available. At obvious levels where many stops cluster, the resulting wave of simultaneous aggression can exhaust liquidity at and around the stop level, filling later orders at progressively worse prices. The further into the wave your stop triggers, the worse the fill. Slippage is not random and it is not a broker problem. It is predictable — it happens most severely at the obvious levels where order clustering is densest.

In the Book 1 chapter

Chapter 7 · What The Chart Is

Stops Are Aggression in Waiting

Every trader uses a stop loss. Most trading education treats this as basic risk management — you set a level, and if price reaches it, you’re out of the trade. Simple protection. A safety net.

From the Blog 1 post

Why You Keep Getting Stopped Out Right Before the Move

There is usually a mechanical explanation for why price moved through your stop before continuing.