When you look at stock quotes, there are numbers after the bid and ask prices for a particular stock. These numbers usually are shown in brackets and they represent the number of shares in a series of 10 or 100 that limit orders pending trade. These numbers are called the bid and ask sizes, and represent the aggregate number of pending orders at specified bid and ask prices.
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For example, suppose that we obtained stock prices for XYZ Corp. and we see the rate of $15.30 (25), and from $15.50 (10). Demand price is the maximum bid entered to purchase shares of XYZ stock, while price is the lowest price entered for the same part. As you can see, there are numbers after the bid and ask prices, and the number of shares that are expected to trade on their prices. Currently, the maximum purchase price of $15.30, there are 2,500 shares offered for purchase, in the aggregate. Aggregation for all orders entered at the same bid price, no matter if coming from the trades person for 2,500 shares, 2,500 people bidding for one share each. The same is true for numbers lower the price.
If these orders are not executed during the trading day, they can be transferred to the next trading day provided that they do not day orders. If these bid and ask orders are day orders, then they will be cancelled at the end of the trading day if they are not populated.
The difference between the two prices is called the BID-ask spread. If the investor buys shares in XYZ, he or she will pay $15.50. If this same investor subsequently liquidated those shares, they will be sold for $15.30. The difference is a loss for the investor.
For more information, see the basics of the stock market: how to read a stock table/Quote.