What it is
Add up the shares traded on the days a stock closed higher. Then add up the shares traded on the days it closed lower. Use the last fifty trading days. If more shares changed hands on the up days, buyers have been the more aggressive side for two and a half months. That holds whatever the price chart looks like day to day.
How Breakaway uses it
U/D VOL fires when up-day volume beats down-day volume over the last 50 trading days. It is a participation trait and one of the four the card labels predictive. It describes a condition that builds before a move rather than the move itself.
How to read it
The trait is quiet by nature, and it is rarely the reason you notice a stock. Its value is in backing up or contradicting the others. A breakout with U/D VOL lit has weeks of steady buying behind it. A breakout with U/D VOL dark is running on one day's excitement. That is a different bet.