What It Means
Slippage is the difference between an order's expected price and the price it actually fills at — the gap between what you clicked and what you got.
How It Works
Slippage shows up most on market orders and triggered stop-loss orders in thin or fast-moving markets, where the price moves between the moment an order is sent and the moment it executes. Wider bid-ask spreads and low liquidity make it worse; a liquid large-cap stock during normal hours rarely slips more than a few paise.
Example
You place a market order to buy at a quoted price of ₹1,200. By the time it fills, the price has moved to ₹1,203 — that ₹3 gap is slippage.