Volume, or trading volume, is the number of units traded in a market during a given time. It is a measurement of the number of individual units of an asset that changed hands during that period.
Each transaction involves a buyer and a seller. When they reach an agreement at a specific price, the transaction is recorded by the facilitating exchange. This data is then used to calculate the trading volume.
This also means that for a stock, for example, the trading volume refers to the number of individual stocks that were traded during the measured period. So if 100 shares are traded in one trading day, the daily volume of the stock is 100 shares.
Traders tend to use the volume indicator as an attempt to gain a better understanding of the strength of a given trend. If volatility in price is accompanied by high trading volume, it may be said that the price move has more validity. Conversely, if a price move is accompanied by low trading volume, it may indicate weakness of the underlying trend.
Price levels with historically high volume can also give traders an indication regarding where the best entry and exit points could be located for a specific trade setup.
Typically, a rising market should see increasing volume, indicating continuous buyer interest to keep pushing prices higher. Increasing volume in a downtrend may indicate increasing sell pressure.
Reversals, exhaustion moves, and sharp changes in price direction are often accompanied by a high volume spike, as these tend to be the times when the highest amount of buyers and sellers are active in the market.