BollingerBands

Commonly abbreviated as BBands or BB.
Is a volatility indicator.
Is computed using the closing price.
Returns three time series consisting of a 20-period moving average of the closing price and bands that are two standard deviations above and below the moving average.
FinancialIndicator["BollingerBands", n, b] uses period n moving averages and bands b standard deviations from the moving average.
The first values in the time series are computed using partial periods.