Basics · Mechanics
The Stock Market and What a Price Is
A quoted price is the last completed trade, a fact about one transaction, not a valuation and not a price you can necessarily get. Everything on this site is computed from those numbers, so it is worth knowing what they are.
Two markets, and only one of them is here
The primary market is where securities are issued: a company sells shares and receives the proceeds. It happens once per issue and the money reaches the company.
The secondary market is everything afterwards, existing shares changing hands between investors, with nothing reaching the company at all. Essentially every number on this site comes from the secondary market, and that fact explains the property that the volume page is about: shares are transferred rather than created, so every share bought was sold by somebody.
What "the price" leaves out
A single quoted price hides two numbers that decide what it is worth knowing. The bidis the highest price someone is currently willing to pay; the offer is the lowest at which someone will sell. You transact at those, and the last trade is history.
Where the trading happens
A listed security in the United States does not trade in one place. It trades on several exchanges simultaneously, plus a substantial share executed off-exchange by wholesalers and alternative venues, with all of it reported to a single consolidated tape.
The consequence for anyone reading volume figures is direct: the exchange a company is listed on is frequently a minority of its own security’s volume, so a single-venue figure is a fraction of the total and the fraction differs between instruments. The basics page sets out the composition, and the short-volume study works through what one slice of the tape does and does not tell you, using real published data.
Who is on the other side
The picture of two investors meeting is largely historical. A large share of retail order flow is executed by wholesalers who take the other side themselves, and automated market makers quote continuously on the exchanges, so the counterparty to most trades is an intermediary managing inventory rather than someone with a view.
That matters for one family of measures in particular. Trade-size analysis, inferring participant type from the size of prints, was built when a large order arrived as a large trade. Orders are now routinely split into many small executions, so a small print no longer implies a small participant, and the trade-size page works through what survives of the method.
The close, and the auction that sets it
A closing price is not simply the last continuous trade on most venues: it comes from a closing auction, a separate mechanism that matches accumulated orders at one price at a single moment. That is why the close is the price with the most agreement behind it, and it is a good reason to prefer closes over intraday snapshots for anything being compared over time.
It also has a practical consequence for volume work. The auction arrives as one print from a queue built beforehand, its share of the session has grown, and on index rebalance dates it can dwarf everything else. Anything computed from continuous trading, an intraday volume profile above all. Should keep the auction as its own line rather than folding it into the final interval.
What a halt does to the record
Trading in a security can be stopped (for pending news, for a volatility breach, or by the regulator), and a halt leaves a specific mark on the data that is easy to misread.
During a halt there are no prints, so nothing is recorded: no price, no volume, and no indication in a daily series that the session was interrupted. When trading resumes, the whole move arrives in one step, which can span what would otherwise have been two sessions. Any measure computed from consecutive closes treats that as an ordinary bar, and any range-based measure treats a gap as a small range unless it uses true range, which accounts for the previous close.
The practical consequence appears on the screens: a biggest-losers list can omit the day's worst outcomes entirely, because the instruments concerned did not print a normal close, and then report them the following day at a size that belongs to two sessions. It is the clearest case on this site of missing data that looks like no data at all.
Price and size are different things
One confusion is worth killing explicitly, because two separate errors on this site trace back to it. A company’s size is its share price multiplied by the number of shares it has issued, and a company chooses how many shares to divide itself into.
So a high share price says nothing about how large the business is. That is why a most-traded list ranked by share count is substantially a list of cheap stocks, and why the Dow’s price weighting gives a mid-sized company with expensive shares more influence than a far larger one with cheap shares. Both are arithmetic consequences of confusing a price with a size, and both are invisible if the distinction is not held firmly.
Frequently asked questions
What is a quoted price?
The price at which the last trade in that security was completed. It is a fact about one transaction between two parties, and it is not a valuation, not an offer, and not necessarily a price you can transact at now. What you can transact at is the bid and the offer — two numbers, not one — and the gap between them is the spread.
Why does the distinction matter for this site?
Because every measure here is computed from prices, and the assumption that a price is a single reliable number is what makes people trust indicator readings on instruments where it is not. On a thinly traded issue the last trade can be hours old, the two available prices can be far apart, and a "move" between two closes can be an artefact of which side of the spread each print landed on rather than a change in what anyone thinks.
What is the primary market against the secondary market?
The primary market is where securities are issued, a company sells shares and receives the proceeds. The secondary market is everything afterwards: existing shares changing hands between investors, with no money reaching the company. Essentially all the trading this site is about is secondary, which is worth knowing because it explains why volume is symmetric: shares are transferred, not created.
Who is on the other side of a trade?
Increasingly, an intermediary rather than another investor. A substantial share of retail order flow is executed by wholesalers who take the other side and manage the resulting position, and automated market makers quote continuously on the exchanges. That changes the interpretation of some older measures, trade-size analysis in particular, because a large order is now routinely split into many small executions, and a small print no longer implies a small participant.
Where does the trading actually happen?
Across many venues at once. In the United States a listed security trades on multiple exchanges plus a large off-exchange share, all reported to a consolidated tape, and the exchange the company is listed on is frequently a minority of its own volume. That is why this reference says consolidated volume when it means the total, and why a single-venue figure cannot be compared with a tape figure.
What is the closing auction?
A separate mechanism that matches accumulated orders at one price at the end of the session, rather than continuous trading. It has grown into a substantial share of the day’s volume, it produces a single print, and on index rebalance dates it can be enormous. Anything computed from continuous trading, an intraday volume profile especially, should keep it separate rather than folding it into the last interval.
Does a higher price mean a bigger company?
No, and the confusion is behind two of the more persistent errors on this site’s subject. Size is the share price multiplied by the number of shares, and a company can choose how many shares to divide itself into. That is why a share-volume ranking is largely a list of cheap stocks, and why the Dow’s price weighting measures something other than size.
What can a price support, then?
A great deal, carefully. A series of closes is the most-agreed record of what a market decided, and everything in this reference is built on one. The qualifications are the ones above: know how liquid the instrument is, know that a close is one print rather than a consensus, and use adjusted prices so a split does not read as a collapse. Those three checks cost nothing and remove most of the ways a price series misleads.