Volatility measures how much a fund's value shakes from one period to the next. Two funds can end the year with the same return, one travelling an almost straight line and the other through sharp waves — the second has higher volatility, and its ride is harder on both nerves and financial plans.
Statistically, volatility is the standard deviation of the fund's returns, usually annualized. A rough reading: a fund averaging 7% with 10% volatility will land between −3% and +17% in about two out of three years, and outside that range in the rest.
Volatility is not inherently bad — assets with higher long-run returns tend to be more volatile. What matters is the match between a fund's volatility and your ability to sit through declines without selling at the bottom, given your time horizon.
On Fundtrics fund pages, the risk-level label (low/medium/high) is grounded in the fund's actual return volatility — a money market fund whose price barely moves is labelled low-risk regardless of its category.