Volatility Formula

 

Hello peeps, im just wondering if theres any actual equation for volatility? I've seen it used and measured in various ways and i know you can measure the total change in a day vs the current value, or change vs range, or high - low / volume or some nominal value based on time etc but is there an actual equation or is it subjective? i know statistically about variance but variance is absolute in terminology whereas volatility seems more of a vague idea thats not strictly defined.

 

Regards.