This article explains the common equity order types as a concept. It is educational and general, a description of the tools an exchange offers and the tradeoffs between them, not personalised investment advice. Nothing here is a recommendation to buy or sell any security or to use any particular order.
An order type is not a decision about what to trade; it is an instruction about how the trade should be handled once it is sent. Every equity order sits somewhere on a single axis: how badly does the trader want to be filled versus how much does the price matter? Market orders take the fill and accept the price; limit orders name the price and accept that they might not fill. Stops arm on a trigger, and the closing and opening auctions fill a whole day’s demand at one clearing price. What follows is what each order does, the tradeoff it makes, and the slippage that lives in the gap between the expected price and the filled price.
The short version
The common equity order types are market (certain fill, uncertain price), limit (certain price bound, uncertain fill), stop and stop-limit (conditional orders that arm at a trigger), and the auction orders MOC and MOO (fill at the official close or open). They all trade fill certainty against price control.
The sections below define each one, starting with the single axis that organises the whole family, and close with slippage, the gap between the expected price and the filled price.
The one tradeoff behind every order type
Before the individual types, the axis they all sit on. Every order answers one question: if a guaranteed fill and a guaranteed price cannot both be had, which one is given up? A market order chooses the fill and surrenders control of the price. A limit order chooses the price and surrenders the guarantee of a fill. Every other order type is a variation on that same trade, or a rule about when to make it. Nothing in the order book delivers certainty on both sides at once, and understanding which side a given order sacrifices is most of what there is to know.
The reason the tradeoff exists is that a stock does not have a single price. It has a bid (the highest price a buyer is currently willing to pay) and an ask or offer (the lowest price a seller will accept), and the gap between them is the spread. A buyer who insists on filling right now crosses the spread and pays the ask; a seller in a hurry hits the bid. Order types are, in large part, tools for deciding how a trader interacts with that spread and with the depth of resting orders behind it.
Market orders: certain fill, uncertain price
A market order says “fill me now, at whatever the best available price is.” It is the most certain way to get done: for any reasonably liquid stock a market order is filled almost instantly, because it simply accepts the prices already resting in the order book. What it does not promise is which price. In a fast-moving or thin market, the quote from a moment ago may not be the quote it fills at, and a large market order can “walk the book,” consuming the best-priced shares and then filling the rest at progressively worse prices. The certainty is real; the cost is that the market, not the trader, holds the pen on price.
Limit orders: protected price, uncertain fill
A limit order is the mirror image. It names a worst acceptable price, a ceiling for a buy, a floor for a sell, and will fill only at that price or better. A buy limit will never pay more than the limit; a sell limit will never accept less. The tradeoff runs the other way: a guaranteed worst-case price and no guarantee of a fill. Note that the control is over the price bound, not the exact fill: a limit can execute at the limit or better, but never worse. If the market never trades at the limit, or trades through it so fast the order is not reached, it simply does not fill, and the opportunity can pass. A limit order guards against a bad price at the risk of guarding its way right out of the trade.
Stop and stop-limit orders: conditional orders that arm at a trigger
A stop order (often called a stop-market or stop loss) is not live in the book until a condition is met. The trader sets a trigger, or stop, price; the order does nothing while price stays on one side of it, and the moment the market trades at or through the trigger, the stop becomes a market order and fills at the best available price. It is the standard tool for automating an exit: an instruction to get out if price reaches a level, without watching the screen. Because it converts to a market order, it inherits the market order’s tradeoff, the fill is near-certain once triggered, but the price is not, and in a sharp move a stop can fill well past its trigger.
A stop-limit order swaps that final behaviour. It arms at the same kind of trigger, but instead of turning into a market order it turns into a limit order at a specified price. This caps how bad the fill can be, but it reintroduces the limit order’s risk: if price gaps straight through both the trigger and the limit, the order arms and then never fills, leaving the position open in exactly the fast move the stop was meant to handle. Stop versus stop-limit is the fill-certainty-versus-price tradeoff applied to the exit itself.
The auction orders: market-on-close and market-on-open
Continuous trading is not the only way shares change hands. Major equity exchanges run call auctions at the start and end of the session that gather up buy and sell interest and cross it all at a single price, the one that clears the most volume. Two order types target those auctions directly.
A market-on-close (MOC) order is an instruction to participate in the closing auction and fill at the official closing price. A market-on-open (MOO) order does the same for the opening auction. Their appeal is twofold. First, the closing and opening crosses are typically the deepest, most liquid moments of the day, so a large order can often be absorbed with less price impact than the same order worked through the thinner continuous session. Second, they fill at the day’s official mark, the print that indices, funds and benchmarks reference, which is why so much institutional volume concentrates there. The tradeoff is that the order accepts whatever that single auction price turns out to be, and (depending on the venue and order type) these orders often cannot be cancelled close to the cross.
At a glance
| Order type | What it does | The tradeoff |
|---|---|---|
| Market | Fills immediately at the best available price. | Certain fill, uncertain price (can slip in fast or thin markets). |
| Limit | Fills only at a set price or better. | Price protected (no worse than the limit), uncertain fill (may never execute). |
| Stop (stop-market) | Becomes a market order when the trigger price trades. | Near-certain fill once triggered, uncertain price past the trigger. |
| Stop-limit | Becomes a limit order at a specified limit price when the trigger price trades. | Caps the fill price, but may not fill if price gaps through. |
| Market-on-close (MOC) | Fills at the official closing auction price. | Deep, official-price fill, but bound to the single cross price. |
| Market-on-open (MOO) | Fills at the official opening auction price. | Deep, official-price fill, but bound to the single cross price. |
Slippage: the gap between the expected price and the filled price
Slippage is the difference between the price a trader expected and the price actually filled, the natural consequence of a moving market and a finite order book. Market orders and triggered stops slip when the best-priced shares are consumed and the rest fill deeper, or when the quote moves in the instant between sending and filling. The more illiquid the name, the wider the spread, and the larger the order relative to normal volume, the more slippage tends to matter. This is the practical reason order-type choice is not cosmetic: the same intended trade can end up at a meaningfully different price depending on how it interacts with the spread and the depth behind it.
How a systematic process treats execution
For a rules-based system, order type is a fixed part of the method, chosen once and applied the same way every day so that execution does not quietly become a second, undocumented strategy. Shishin fills its high-volume names market-on-close: rather than chasing an intraday print, the intended size is sent into the closing auction, where liquidity is deepest and the official closing price is set. That choice does two things at once. It lets the largest, most liquid names absorb the intended size at the day’s benchmark mark instead of pushing price around in the thinner continuous session, and it keeps the entry disciplined: a name is scored and acted on at the close rather than getting chased on an open gap that has already run. The mechanics of that closing-auction execution, and how it shows up in the realised record, are described on the track record page, with the underlying signals attested and independently checkable at verify. It is a single example of the same principle this whole article describes, choosing where on the fill-versus-price axis to sit, made once and made in advance.
The limits
A few caveats keep the picture honest. Exact order-type behaviour varies by exchange and broker: cut-off times for MOC and MOO orders, whether a triggered stop is visible to the market, and how partial fills are handled all differ between venues, so the definitions here are the general shape rather than a universal rulebook. Order types are also often combined and qualified, with time-in-force instructions (day, good-till-cancelled) and conditions (fill-or-kill, all-or-none) layered on top. And crucially, no order type improves the underlying decision: a well-chosen order can only reduce the friction between an intention and its execution, never make a poor trade a good one. The order type governs the how; it is silent on the whether.
So, which order type is “best”?
There is no best order type, only a best fit for a given intention, because each one deliberately sacrifices something. If certainty of execution matters most, the market family delivers it and accepts price risk. If price control matters most, the limit family delivers that and accepts the risk of no fill. Stops automate a conditional exit and inherit whichever tradeoff (market or limit) they convert into. The auction orders trade the flexibility of continuous trading for depth and an official price. Understanding the family is really understanding one axis, fill certainty versus price control, and knowing which end of it each tool sits on.
Sources & further reading
- U.S. Securities & Exchange Commission (Investor.gov). “Order Types” and “Stock Purchases and Sales: Long and Short.” Plain-language definitions of market, limit and stop orders and their risks.
- Harris, L. Trading and Exchanges: Market Microstructure for Practitioners. Oxford University Press, on the bid-ask spread, order types, and how call auctions clear.
- For how execution fits into a published, rules-based process: how a trading signal works and how breakout setups work (which discusses filling on the close to avoid chasing gaps).