Volume counts transactions, not participants or direction. Every share traded has a buyer and a seller, so high volume never means "more buyers than sellers"; it means more disagreement was resolved at those prices.
Its main use is confirmation. A breakout on twice the average daily volume reflects genuine repositioning. The same breakout on a quiet afternoon is far more likely to fail, because too few holders changed their mind for the new level to hold.
Compare volume to the same asset’s own history, never across assets. Ten million shares is a dead session in Apple and an extraordinary one in a mid cap. Expect predictable distortions on index rebalance days and on the quarterly triple witching expiry.