Volatility

Volatility is a measure of how much and how quickly the price of an investment moves up and down over time. A highly volatile stock can swing sharply in either direction over short periods, while a low-volatility stock tends to move more gradually.

Volatility is not the same thing as risk in the sense of losing money permanently, a volatile stock can still end up higher over the long run, but it does mean an investor has to be prepared to stomach larger short-term swings, both up and down, along the way.