An order is an instruction to buy or sell a financial instrument under stated conditions. You submit it to a broker or trading venue, which tries to execute it according to your price, size and timing settings.
Think of an order as the request, and a trade as the outcome. Some orders fill immediately, some queue on the order book and wait, and some never trade at all.
What an order includes and where it goes
Every order carries a few essentials:
- Side: buy or sell.
- Instrument: the asset and venue symbol.
- Quantity: number of shares, contracts or units.
- Price: only for price‑limited orders.
- Order type: such as market, limit or stop.
- Time in force: how long it stays active.
- Optional flags: for routing, visibility or risk control.
From your app or API, the order usually goes to your broker, then to a matching engine or dealer. Many brokers use a smart order router that searches for the best available price across venues. The exact path and features vary by provider and market structure.
On central order books, resting buy and sell orders meet under clear rules, often price then time priority. Some markets also support dealer quotes, auctions and negotiated trades. Not all order types are available everywhere.
Common order types and when traders use them
A market order tells the broker to trade now at the best price available. It prioritises speed over price control, which can lead to slippage if the book is thin or moving quickly.
A limit order sets the worst price you will accept. A buy limit caps the price you pay, a sell limit sets the minimum you will receive. If your price is not reached, the order can sit on the book and may never fill.
Stop orders are conditional. A stop market order becomes a market order once the stop price is touched. Traders often use it as a stop loss that aims to exit during a drop. A stop limit order becomes a limit order at the trigger, which adds price control but risks no fill in a fast move.
Trailing stops follow price by a fixed amount or percentage. If you buy at 100 with a 5 percent trailing stop, the stop will rise as the market makes new highs, then trigger if the price falls that distance from the latest peak.
Visibility and queueing tools include iceberg (only a small slice is visible, with the rest refreshing), hidden orders that do not display, and post‑only or maker‑only instructions that avoid taking liquidity. Availability depends on the venue.
Time in force and other instructions that shape fills
- Day: expires at the end of the trading session if not filled.
- Good till cancelled (GTC): stays open until you cancel or until a platform cut‑off. Some brokers treat GTC as good for a set number of days.
- Good till date/time (GTD/GTT): expires at a specific date and time.
- Immediate or cancel (IOC): fills what it can instantly and cancels the rest.
- Fill or kill (FOK): must fill in full immediately, otherwise the entire order cancels.
- All or none (AON): requires a full fill, not partials. Often combined with longer time in force, support varies.
- At the open/close: participates only in the opening or closing auction.
These settings decide how long your order can wait, whether partial fills are acceptable and whether it can interact with auctions. They are as important as price, especially for larger sizes.
From order to trade: queueing, partial fills and slippage
When a limit order arrives inside the current spread or beyond the best price, it can execute immediately against resting orders on the other side. If it cannot fully execute, any remainder may rest on the book at your price. If your price is away from the market, it simply queues and waits for price to come to it.
Most venues use price then time priority. At the same price level, earlier orders stand in front of later ones. Your queue position affects how quickly you are likely to get filled if the market trades at your price.
A partial fill is common in active markets. Suppose you place a limit buy for 2,000 shares at 10.00. If only 500 are offered at 10.00 when your order hits, you buy 500 now and 1,500 remain working. If more supply appears at 10.00 later, the remainder can fill in chunks. Each execution is a separate trade, with its own timestamp and price.
Slippage is the difference between your expected price and the execution price. Market orders can slip when quotes move between submission and match, or when the best size is small. Limit orders avoid negative slippage by refusing worse prices, though they can miss a fill completely. Sometimes you receive price improvement, which is a better price than you specified, usually when a counterparty improves the quote to win the trade.
Cancel and replace is normal practice. Traders update a resting limit to chase price, reduce size or adjust to new information. Modifying an order can lose your place in the queue, depending on the venue’s rules.
Costs matter. You pay commissions and exchange or venue fees if applicable, and you cross the bid‑offer spread when taking liquidity. Maker‑taker fee models pay or charge different amounts depending on whether you add or remove orders from the book. Exact charging policies vary by venue and broker.
Risk and strategy orders: stops, OCO and brackets
Orders are not only for entry. They also automate exits and risk control.
- Stop loss: a stop market or stop limit to cap downside.
- Take profit: a limit order to exit at a target level.
- OCO (one cancels the other): links two orders so that a fill on one cancels the other. Commonly pairs a take profit with a stop loss.
- Bracket order: wraps an entry with both a stop and a take profit as OCO, so the position is managed once the entry fills.
- Reduce‑only: ensures the order can only decrease or close an existing position, often used in leveraged products and crypto.
Consider a simple bracket: you buy 1 BTC at 30,000 with a take profit limit at 31,200 and a stop market at 29,400. If price reaches 31,200 the take profit fills and the stop cancels. If instead price falls to 29,400, the stop triggers and the take profit cancels. You can size each child order independently to scale out if desired.
Stops are not guarantees. Gaps and fast markets can see stop market orders fill worse than the trigger level, and stop limits risk no fill. Choice depends on whether you prefer certainty of exit or certainty of price.
How orders interact with liquidity and the order book
Liquidity is the pool of resting orders and willing counterparties at each price. Placing a limit order on the book adds liquidity and can earn maker pricing. Hitting an existing quote removes liquidity and pays the spread.
Quotes are often summarised as the bid and the offer, the best buy and best sell. Your order decides which side you interact with. A market buy lifts the offer. A buy limit at the bid waits in line or encourages sellers to meet it. In auction periods, such as the open and close, orders interact at a single clearing price rather than continuously.
Venue rules and broker settings influence all of this. Some platforms support hidden and pegged orders that track a reference price, some prioritise displayed size over hidden size, and some restrict advanced instructions. Always check what is supported before relying on a specific behaviour.
Across stocks, futures, options and crypto, the principle is the same: an order is your set of conditions for turning an idea into a trade. Choosing the right type and time in force, and understanding how it queues and executes, is as important as picking the instrument in the first place.