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Order types — market vs limit vs stop
Behind every trade is a simple instruction to the exchange, and there are really only three of them. A market order says "fill me now, whatever the price." A limit order says "only at my price or better." A stop order says "do nothing until the price hits a trigger." Each one hands you one guarantee and takes another away — and confusing them is how beginners get surprised.
Three instructions, one order book
Market — certainty of fill, not of price
A market order crosses the spread and takes whatever's available right now. You're guaranteed to fill — but not at a price you chose. On a liquid instrument that's a fraction of a tick; on a thin one, your order walks up the book and you eat slippage. Use it when getting in or out now matters more than the exact price.
Limit — certainty of price, not of fill
A limit order names a price and waits: a limit buy fills only at your price or lower, a limit sell at your price or higher. You'll never pay worse than you asked — the trade-off is it might never fill at all if the market walks away. Use it when price discipline beats urgency, or to add liquidity instead of taking it.
Stop — a dormant trigger
A stop order sits inactive until the price crosses a trigger level, then springs to life — usually as a market order. Its classic job is the stop-loss: "if it drops to 99, get me out." The catch is in the fine print: once triggered it becomes a market order, so in a fast move it can fill well past your trigger. A stop-limit adds a price floor, at the risk of not filling at all.
Market = "now, any price." Limit = "my price, or not at all." Stop = "sleep until the price hits a line, then act." You're always trading speed against price.
Everything more exotic — brackets, trailing stops, iceberg orders — is built from these three. Once you internalise which guarantee each one gives and which it takes, half the confusing behaviour on the tape (and in your own fills) explains itself.