Definition
Realized volatility is calculated from observed historical returns. A common implementation takes daily logarithmic returns, measures their standard deviation over a rolling window, and annualizes the result.
Why annualize?
Annualization converts windows of different lengths to a common scale. For daily crypto data, volatility is commonly multiplied by the square root of 365. The result is a statistical rate, not a forecast of the exact annual price range.
30D, 90D and 1Y
Short windows respond quickly but are noisy. Longer windows change slowly but can lag regime shifts. Comparing multiple windows can reveal whether volatility is expanding or contracting.
High volatility means returns are more dispersed. It does not tell you whether those returns will be positive or negative.