A Technical Analysis tool used to measure the market volatility.It consists of 3 lines. The center line is the 21 day moving average of the price of an Asset.The upper and lower bands are calculated as two standard deviations above and below the center line value.When market becomes volatile the Bollinger Bands expand and when market is less volatile they contract.If the Asset value falls beyond the band,it indicates that the Asset is either overbought or oversold.