What are Bollinger Bands?

Bollinger Bands are a type of price envelope developed by John Bollinger

(Price envelopes define upper and lower price range levels.)

Bollinger Bands are envelopes plotted at a standard deviation level above and below a simple moving average of the price. Because the distance of the bands is based on standard deviation, they adjust to volatility swings in the underlying price.

Bollinger Bands use 2 parameters, Period and Standard Deviations, StdDev.