A volatility envelope indicator with three lines – a 20-period simple moving average (middle band) and upper/lower bands typically 2 standard deviations away. The bands expand when volatility rises and contract when volatility falls. Prices near the upper band often indicate overbought conditions, and near the lower band indicate oversold. Forex EAs use Bollinger Band crossovers or “squeeze” breakouts as signals. In code, MQL uses iBands(), and cAlgo has Indicators.BollingerBands(). Bots may sell at band-touch (when trend is strong) or buy when price breaks above a squeeze.