Order

The unit of instruction in every market. Three things describe any order: what is to be dealt and in which direction, what has to be true before it can execute, and how long it remains valid if that condition is not met. Everything called an order type is a different answer to the second question.

Where the condition is nothing at all, the instruction is a market order and goes to the market on receipt. Where it is a price better than the current market, the instruction is a limit order. Where it is a price beyond the current market, in the direction the market is already moving, the instruction is a stop order. Validity is set separately, by a time in force instruction such as good for the day or good until cancelled. Protective instructions attached to a position, a stop loss and a take profit among them, are orders in the same sense: each is a condition and a resulting instruction, held against a position rather than standing alone.

The distinction that carries most of the confusion is between the trigger and the fill. A level named in an order is the condition on which it becomes executable, not the price at which it will be dealt: once triggered, it is filled at the next price available, which in a fast or gapping market can be some distance away. The second is that an order is a request rather than a guarantee. It is accepted by a counterparty under its own rules, and can be rejected, requoted or filled in part, which is why every platform records what was sent and what came back as two separate things.