Market order
A market order buys or sells straight away at the best available price. Definition, when it is the right choice, and how slippage affects it.
Definition
An order to buy or sell immediately at the best price available on the exchange, which fills almost every time but not always at the last price you saw.
A market order says: buy or sell now, at whatever the best available price is. It takes the best offers in the order book until the order is filled.
Example
BTC's last price is $86,930. You place a market buy for $50. The best seller is at $86,935, and your order fills there. In a calm, liquid market the difference is tiny; in a fast one it can be larger.
Why it matters
A market order's strength is certainty of execution: when you need to get in or out, it gets you there. Its cost is that the price is not fixed. The gap between the expected and actual price is slippage, which grows in fast markets and on coins with thin order books.
How TradeCorgi uses it
Agents use market orders for exits, including stop-losses, because getting out matters more than the exact price. Every backtest charges an allowance for slippage on each order, and the decision log records the price each live order actually filled at.
A common mistake
Placing large market orders on coins with thin order books. The order eats through several price levels and fills well below the last price. On less liquid coins, keep orders small or expect more slippage.