Volatility, in finance, refers to the wiggliness of the time series. You observe the price of a security go up and down over time. If it changes a lot, that’s high vol: unstable, unpredictable. If it changes only a little, that’s low vol: stable, consistent.

There are many ways to define volatility, just as there are different ways to measure distance. Portfolio variation should be measured with a quasimetric (unidirectional metric).

But for all those definitions, it should mean roughly: the magnitude of change in the price, during some time interval.


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