Market order
An order executed at the current available market price. Speed and certainty of a fill at the cost of price control — slippage risk when liquidity is thin.
Definition
A market order is an order executed at the current available market price — its priority is speed and certainty (in a liquid market), at the cost of controlling the exact fill price. In practice you can get a worse price because of the spread and slippage.
Example
NFP news is out and you want to close a long EUR/USD immediately. A market sell executes quickly, but the fill may be several pips worse than the last mid — especially when the spread has widened.
Anti-example / common mistake
Using a market order in an illiquid small-cap, or a second after macro data, “because I have to be in the market”, with no slippage limit. The second mistake: confusing the mid price on the chart with the real ask/bid at entry.
When it makes sense
An emergency exit from risk (a manual stop, a news event) in a liquid instrument — you knowingly pay for speed. An educational setup entry is more often built with a limit order or a conditional stop with invalidation. On the GPW’s illiquid names a market order is more expensive than you think; on CFDs check the broker’s slippage-protection terms (if there are any).