Volatility measures how much a price fluctuates over time, regardless of direction. A stock that swings 5% in either direction on an ordinary day is more volatile than one that typically moves a fraction of a percent — volatility describes the size of the moves, not whether they're up or down.
Higher volatility generally means higher risk in the everyday sense of the word: bigger potential losses over a short window, but also bigger potential gains. It tends to rise sharply around earnings reports, major news, and periods of broad market stress, and settle during calmer stretches.
Volatility is distinct from a stock's long-term trend. A stock can be highly volatile while trending steadily upward over months, or low-volatility while going nowhere — the two describe different things about a price series.