Volume. The higher the relative volume is at a particular price level, the more likely it is that the price level will become significant support or resistance. This should make sense. If support, for example, is a function of the number of buyers willing to purchase the stock at a certain price, then a price level which has attracted high volume in the past is more likely to act as support than the price level that has not attracted volume in the past.

The basic relationship between price and volume is one where volume confirms price. "Confirmation" is a technical analysis term that means to support, or agree with. As with many areas of analysis, technical analysis is a science of looking for coincident indications that your premise about the market is correct. When one indication agrees with another it is called confirmation. For example, if the price of a stock is rising you might anticipate that the stock will continue to go higher. If there is an increase in volume with the increase in price, the increase in volume provides another reason to believe that the price will continue to rise and thereby serves as a confirmation of the price action.