Volume points to the amount of a financial instrument that was traded over a specified period of time. It can refer to shares, contracts or lots. The data is tracked and provided by market exchanges. It is one of the oldest and most popular indicators and is usually plotted in colored columns, green for up volume and red for down volume, with a moving average. It is one of the few indicators that is not based on price. High volume points to a high interest in an instrument at its current price and vice versa.
A sudden increase in trading volume points to a increased probability of the price changing. News events are typical moments when volume can increase. Strong trending moves go hand in hand with an increased trading volume. It can therefore be seen as a measure of strength. One would expect high buying volume at a support level and high selling volume at a resistance level. There are several ways to use volume in a trading strategy and most traders use it in combination with other analysis techniques.