Volume represents the number of trades happening at any given time. It's usually represented as a histogram, or a graph composed of vertical bars, underneath the price chart.
Volume charts are often used in conjunction with the basic types of price charts to illustrate the amount of trading taking place over the same time period depicted in the chart. Higher volume tends to give greater weight to the day's price movements. For instance, a high trading volume on a day when a stock's price increases is more significant than low trading volume on a day when the stock's price increases.
Volume is used as a secondary indicator to price, but heavy volume can signal higher participation in the market and more sustained moves in price. Scottrade reports volume per NASDAQ rules and technical specifications.
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