The short answer
Execution is how your order actually gets filled — and the price you see is not always the price you get. Slippage is the difference between your expected price and your actual fill, common in fast markets and around news. A market order fills at the best available price (which can move against you); a limit order fills only at your price or better (but might not fill at all). Understanding this prevents nasty surprises at the worst moment.
What execution is
Execution is the process of your order being filled by your broker after you click 'buy' or 'sell.' It sounds instant and exact, but in fast-moving markets there can be a small gap between the price you saw and the price you actually get. Understanding how fills work — and where they can go wrong — is part of trading competently.
Market vs limit orders
Two order types illustrate the trade-off. A market order says 'fill me now at the best available price.' It executes almost certainly, but in a fast market the 'best available price' can be worse than what you saw a moment ago. A limit order says 'fill me only at my price or better.' It protects your price, but it might not fill at all if the market moves away.
This is the fundamental execution trade-off: certainty of fill (market) versus certainty of price (limit). See order types for the full range.
Slippage: the gap between seen and got
Slippage is the difference between the price you expected and the price you actually got on a market order. It happens because prices move continuously and, in the instant between your click and the fill, the market can shift. Slippage can be negative (a worse fill) or occasionally positive (a better one), but around fast events it is usually against you.
Slippage is worst in thin, fast conditions: major news releases, session opens, and low-liquidity hours. A stop-loss can also slip, filling worse than its level in a violent move — an important risk to understand.
Requotes
On some execution models you may get a requote: instead of filling your order, the platform comes back offering a new price because the market moved. You then accept or decline. Frequent requotes are frustrating and can be a sign of a poor broker or slow execution, so they are worth watching.
Managing execution risk
You cannot eliminate slippage, but you can manage it. Be cautious around news — spreads widen and slippage spikes, so trading through a major release is high-risk. Use a broker with good execution and reasonable spreads. Size for the worst case — assume a stop might slip in a fast move, and do not rely on it filling exactly. And test how your platform executes on a demo and small live size.
Understanding execution turns a nasty surprise into an expected, managed cost. This is education, not advice.
Frequently Asked Questions
What is slippage in trading?
The difference between the price you expected and the price you actually got when an order fills. It happens because prices move continuously, and in the instant between your click and the fill the market can shift — usually against you around fast events.
What is the difference between a market and limit order?
A market order fills now at the best available price, which can be worse than you saw in a fast market. A limit order fills only at your price or better, protecting your price but risking not filling at all. It is certainty of fill versus certainty of price.
When is slippage worst?
In thin, fast conditions — major news releases, session opens and low-liquidity hours. Spreads widen and slippage spikes around events, and a stop-loss can also slip, filling worse than its level in a violent move.
What is a requote?
When, instead of filling your order, the platform comes back offering a new price because the market moved, and you accept or decline. Frequent requotes are frustrating and can indicate a poor broker or slow execution.
Can a stop-loss slip?
Yes. In a fast, violent move a stop-loss can fill worse than its level, because it becomes a market order once triggered and fills at the next available price. Size for that worst case and do not assume a stop fills exactly. This is education, not advice.