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.