Risk
Volatility
Volatility is how widely a price has swung, regardless of whether those swings matched the market.
Beta asks about co-movement with the market. Volatility asks how large the moves were. A stock can be volatile on its own news and still have a moderate beta if those moves were idiosyncratic. Traders care about volatility because it sets the size of a reasonable position and the width of a stop. Long-term owners care because a volatile price tests whether they will still be owners at the bottom.
The most-volatile list on Stocklytics ranks names by beta and by the size of the latest move, which is a practical screen for stocks that are actually moving, not a formal options-implied volatility. Implied volatility, from option prices, is the market's forecast. Realized volatility is what already happened. They diverge when the market expects a catalyst.
Formula
A common measure: the annualized standard deviation of returns
Live example
Apple Inc. (AAPL) last printed at $345.33 with a market cap of $5.04T. Beta on the row is 1.07. The latest session move is unavailable.
Related
Beta · Drawdown · 52-Week Range
See it on a list: best stocks · screener
Questions
Is high volatility bad?
It is a cost if you need the money soon or if it shakes you out. It is the source of opportunity if your thesis is intact and the price moved without the business changing.
How is this different from beta?
Volatility is the size of the stock's own moves. Beta is the portion of those moves that lined up with the market.