It typically boils down to some measure of the non-directional range of moves during some period; either present, historical, or expected. Opportunity exists in both high volatility as well as low volatility periods. Fear exploiters are generally operating on the assumption that high volatility regimes are profitable more quickly, but there are always trade offs in such approaches-- greater reward's twin is greater risk.
I see what you're saying. I expressed it that way because just saying variance in price would not be sufficient; variance in price to me just mean that the best bid/offer changes; whenever the quote changes, price has changed. Volatility results not only in more quote changes, but in a wider range.
Volatility is the daily range from high to low, it's both something good and bad, it creates opportunites but also create risk as wild price moves hit your stops and create losses. As soon as I'm into a position I want a stable trend in the direction I'm trading, not volatility.