Volatility is sort of a "how scary it is"-scale for a rollercoaster. Small volatility – low rises and dips. Bigger volatility – stronger ups and downs.
In other words, the greater the volatility of a stock or fund is, the bigger swings in its value have been in the past.
This means that investments with higher volatility are usually viewed as riskier. Lower volatility goes hand-in-hand with lower risk.
Volatility is a math term that helps to compare investments. If the invested money may be needed within a year or two, it's better to pick investments with lower volatility.