What is the difference between a stop order and a stop limit order?
Stop order is shorter term for stop-loss order.  The point being that is intended as a protective measure.  A buy stop order would be used to limit losses when an investor has sold a stock short.  (Meaning that they have borrowed stock and sold it, in hopes that they can take advantage of a decline in the stock's price by replacing the borrowed stock later at a cheaper price.  The idea is to limit losses due to a rising stock price.)  Meanwhile, a sell stop order would be used to limit losses on a stock that an investor actually owns, by selling it before the price declines further. The important thing to keep in mind about stop orders is that they turn into market orders when the stop price is reached.  This means that they will be filled at the best available price when the order is actually executed.  In fast moving markets, this can be a price that is quite different from the stop price. A limit order allows an investor to ensure that they do not buy/sell a stock at more/less than the specified amount. The thing to keep in mind is that a limit order is not guaranteed to execute. A stop-limit order is a combination of a stop-loss order and limit order, in that it becomes a limit order (instead of a market order) when the stop price is reached. Links to definitions: Stop order Stop-limit order Limit order Market order "An attempt at a simple answer for the normal investor: A normal investor buys stock then later sells that stock. (This is known as ""going long"", as opposed to ""going short"").  For the normal investor, a stop order (of either kind) is only used when selling. A stop-loss sell order (or stop sell) is used to sell your stock when it has fallen too much in price, and you don't want to suffer more losses.  If the stock is at $50, you could enter a stop sell at $40, which means if the stock ever falls to $40 or lower, your stock will be sold at whatever price is available (e.g. $35). A stop-loss limit sell order (or stop limit sell) is the same, except you are also saying ""but don't sell for less than my limit price"".  So you can enter a stop limit sell at $40 with a limit of $39, meaning that if the stock falls to $40, you will then have a limit order in effect to sell the stock at $39 or higher.  Thus your stock will never be sold at $35 or any value below $39, but of course, if the stock falls fast from $40 to $35, your limit sell at $39 will not be done and you will be left still owning the stock (worth at that moment $35, say)."
A trailing stop will sell X shares at some percentage below the current market price.  Putting in this order with a 10% trailing stop when the stock price is $50 will sell the stock when it hits $45.  It's a market order at that point (see below). A stop order will sell the stock when it reaches a certain price.  The stop order becomes a market order when the magic price is hit.  This means that you may not sell it at or below your price when the order is executed.  But the stock will sell faster because the trader must execute. A stop limit order is the same as a stop order, except the stock won't be sold if it can't be gotten for the price.  As a result, the sell may not be executed. More information here. Probing for hidden limit orders usually involves sending the orders and then cancelling them before they get filled if they don't get filled. With trades actually going through multiple times for small amounts it looks more like a VWAP strategy where the trader is feeding small volumes into the market as part of a larger trade trying to minimize average cost. It could be probing but without seeing the orders and any cancels it would be difficult to tell. edit: I just had another thought; it could possibly be a market maker unwinding a bad position caused by other trading. Sometimes they drip trades into the market to prevent themselves from hitting big orders etc. that might move back against them. This is probably not right but is just another thought. source: I work for an organization that provides monitoring for these things to many large trading organizations. "Your logic breaks down because you assume that you are the only market participant on your side of the book and that the participant on the other side of the book has entered a market order. Here's what mostly happens: Large banks and brokerages trading with their own money (we call it proprietary or ""prop"" trading) will have a number of limit (and other, more exotic) orders sitting on both sides of the trading book waiting to buy or sell at a price that they feel is advantageous. Some of these orders will have sat on the book for many months if not years. These alone are likely to prevent your limit orders executing as they are older so will be hit first even if they aren't at a better price.  On more liquid stocks there will also be a number of participants entering market orders on both sides of the book whose orders are matched up before limit orders are matched with any market orders. This means that pairing of market orders, at a better price, will prevent your limit order executing. In many markets high frequency traders looking for arbitrage opportunities (for example) will enter a few thousand orders a minute, some of these will be limit orders just off touch, others will be market orders to be immediately executed. The likelihood that your limit order, being as it is posited way off touch, is hit with all those traders about is minimal. On less liquid stocks there are market makers (large institutional traders) who effectively set the bid and offer prices by being willing to provide liquidity and fill the market orders at a temporary loss to themselves and will, in most cases, have limit orders set to provide this liquidity that will be close to touch. They are paid to do this by the exchange and inter-dealer brokers through their fees structure. They will fill the market orders that would hit your limit if they think that it would provide more liquidity in such a way that it fulfils their obligations. Only if there are no other participants looking to trade on the instrument at a better price than your limit (which, of course they can see unless you enter it into a dark pool) AND there is a market order on the opposite side of the book will your limit order be instantaneously be hit, executed, and move the market price." "After learning about things that happened in the ""flash crash"" I always use limit orders. In an extremely rare instance if you place a market order when there is a some glitch, for example some large trader adds a zero at the end of their volume, you could get an awful price.  If I want to buy at the market price, I just set the limit about 1% above the market price. If I want to sell, I set the limit 1% below the market price. I should point out that your trade is not executed at the limit price. If your limit price on a buy order is higher than the lowest offer, you still get filled at the lowest offer. If before your order is submitted someone fills all offers up to your limit price, you will get your limit price. If someone, perhaps by accident, fills all orders up to twice your limit price, you won't end up making the purchase. I have executed many purchases this way and never been filled at my limit price." TD will only sell the stock for you if there's a buyer. There was a buyer, for at least one transaction of at least one stock at 96.66. But who said there were more? Obviously, the stocks later fell, i.e.: there were not that many buyers as there were sellers. What I'm saying is that once the stock passed/reached the limit, the order becomes an active order. But it doesn't become the only active order. It is added to the list, and to the bottom of that list. Obviously, in this case, there were not enough buyers to go through the whole list and get to your order, and since it was a limit order - it would only execute with the limit price you put. Once the price went down you got out of luck.  That said, there could of course be a possibility of a system failure. But given the story of the market behavior - it just looks like you miscalculated and lost on a bet. Although this is possible with many brokers, it's not advisable. In many cases you may end up with both trades executed at the same time. This is because during the opening, the stock might spike up or down heavily, bid/ask spread widens, and both of your orders would get picked up, resulting in an instant loss. Your best bet is to place the stop manually sometime after you get filled. The obvious thing would happen. 10 shares change owner at the price of $100. A partially still open selling order would remain. Market orders without limits means to buy or sell at the best possible or current price. However, this is not very realistic. Usually there is a spread between the bid and the ask price and the reason is that market makers are acting in between. They would immediately exploit this situation, for example, by placing appropriately limited orders. Orders without limits are not advisable for stocks with low trading activity. Would you buy or sell stuff without caring for the price? "Correcting Keith's answer (you should have read about these details in the terms and conditions of your bank/broker): Entrustment orders are like a ""soft"" limit order and meaningless without a validity (which is typically between 1 and 5 days). If you buy silver at an entrustment price above market price, say x when the market offer is m, then parts of your order will likely be filled at the market price.  For the remaining quantity there is now a limit, the bank/broker might fill your order over the next 5 days (or however long the validity is) at various prices, such that the overall average price does not exceed x. This is different to a limit order, as it allows the bank/broker to (partially) buy silver at higher prices than x as long as the overall averages is x or less.  In a limit set-up you might be (partially) filled at market prices first, but if the market moves above x the bank/broker will not fill any remaining quantities of your order, so you might end up (after a day or 5 days) with a partially filled order. Also note that an entrustment price below the market price and with a short enough validity behaves like a limit price. The 4th order type is sort of an opposite-side limit price: A stop-buy means buy when the market offer quote goes above a certain price, a stop-sell means sell when the market bid quote goes below a certain price. Paired with the entrusment principle, this might mean that you buy/sell on average above/below the price you give. I don't know how big your orders are or will be but always keep in mind that not all of your order might be filled immediately, a so-called partial fill.  This is particularly noteworthy when you're in a pro-rata market." Depending on your strategy, it could be though there is also something to be said for what kind of order are you placing: Market, limit or otherwise? Something else to consider is whether or not there is some major news that could cause the stock/ETF to gap at the open.  For example, if a company announces strong earnings then it is possible for the stock to open higher than it did the previous day and so a market order may not to take into account that the stock may jump a bit compared to the previous close.  Limit orders can be useful to put a cap on how much you'll pay for a stock though the key would be to factor this into your strategy of when do you buy. Exchange-traded funds are bought and sold like stocks so you'd be able to place stop orders on them just like you could for individual stocks. For example, SPY would be the ticker for an S & P 500 ETF known as a SPDR. Open-end mutual funds don't have stop orders because of how the buying and selling is done which is on unknown prices and often in fractional shares. For example, the Vanguard 500 Index Investor shares(VFINX) would be an example of an S & P 500 tracker here. "The SEC reference document (PDF) explains order types in more detail. A fill-or-kill order is neither a market order nor a limit order; instead it's something in between. A market order asks to be filled at the best available price, whatever that price might be when the order gets to the exchange.  Additionally, if there are not enough counterparties to fill the order at the best available price, then part of the order may be filled at a worse price.  This all happens more or less immediately; there's no way to cancel it once it has been placed. A limit order asks to be filled at a particular price, and if no counterparties want to trade at that price right now, then the order will just sit around all day waiting for someone to agree on the price; it can be canceled at any time. A fill-or-kill order asks to be filled at a particular price (like a limit order), but if that price or a better one is not currently available then the order is immediately canceled.  It does not accept a worse price (the way a market order does), nor does it sit around waiting (the way a limit order does).  Since the exchange computes whether to ""fill"" or ""kill"" the order as soon as it is arrives, there's also no way to cancel it (like a market order)." When you place a bid between the bid/ask spread, that means you are raising the bid (or lowering the ask, if you are selling). The NBBO (national best bid and offer) is now changed because of your action, and yes, certain kinds of orders may be set to react to that (a higher bid or lower ask triggering them), also many algorithms (that haven't already queued an order simply waiting for a trigger, like in a stop limit) read the bid and ask and are programmed to then place an order at that point. The purpose of a market order is to guarantee that your order gets filled. If you try to place a limit order at the bid or ask, by the time you enter your order the price might have moved and you might need to keep amending your limit order in order to buy or sell, and as such you start chasing the market. A market order will guarantee your order gets executed. Also, an important point to consider, is that market orders are often used in combination with other orders such as conditional orders. For example if you have a stop loss (conditional order) set at say 10% below your buy price, you might want to use a market order to make sure your order gets executed if the price drops 10% and your stop loss gets triggered, making sure that you get out of the stock instead of being stuck with a limit order 10% below your buy price whilst the stock keeps falling further. "There needs to be a buyer of the shares you are offering.  There are a lot of feature rich options for buying and selling.  I don't understand them all in depth, but for example on TD Ameritrade here are some of the order types ""Limit"", ""Market"", ""Stop Market"", ""Stop Limit"", ""Trailing Stop %"", ""Trailing Stop $"".  This web page will explain the different order types https://invest.ameritrade.com/cgi-bin/apps/u/PLoad?pagename=tutorial/orderTypes/overview.html Stock with a higher volume will allow your trade to execute faster, since there are more frequent trades than stocks with lower volume. (UPDATE: More specifically, not more frequent trades, but more shares changing hands.) I'm a bit of a noob myself, but that's what I understand." "What you are saying is a very valid concern.  After the flash crash many institutions in the US replaced ""true market orders"" (where tag 40=1 and has no price) with deep in the money limit orders under the hood, after the CFTC-SEC joint advisory commission raised concerns about the use of market orders in the case of large HFT traders, and concerns on the lack of liquidity that caused market orders that found no limit orders to execute on the other side of the trade, driving the prices of blue chip stocks into the pennies.  We also applaud the CFTC requesting comment regarding whether it is   appropriate to restrict large order execution design that results in   disruptive trading. In particular, we believe there are questions   whether it is ever appropriate to permit large order algorithms that   employ unlimited use of market orders or that permit executions at   prices which are a dramatic percentage below the present market price   without a pause for human review So although you still see a market order on the front end, it is transformed to a very aggressive limit in the back end. However, doing this change manually, by selling at price 0 or buying at 9999 may backfire since it may trigger fat finger checks and prevent your order from reaching the market.  For example BATS Exchange  rejects orders that are priced too aggressively and don't comply with the range of valid prices.  If you want your trade to execute right now and you are willing to take slippage in order to get fast execution, sending a market order is still the best alternative."