Volatility
How sharply and quickly prices move.
High volatility means big, fast swings in either direction. It reflects uncertainty and often rises during stress.
Volatility measures how much and how fast a price swings, in either direction. High volatility means large, quick moves; low volatility means a quiet, drifting market. It is a measure of movement, not direction, so a market can be highly volatile whether it is rising or falling.
It tends to spike during stress and fear, which is why the VIX, an index of expected S&P 500 volatility, is nicknamed the fear gauge. For a trader, volatility cuts both ways: it creates the price movement that opportunity depends on, but it also widens the range a stop has to survive, so position sizing has to account for it. The same dollar risk needs a smaller position when volatility is high.