Bollinger Bands represent the average expected fluctuations over 20 days set to 2 standard deviations. A breakout of the band is very often a sign of a trend reversal in the short term.

Should the two bands contract, it indicates a strong drop in volatility, signaling that the market is about to trend (positively or negatively). One of the oscillators (theScreener's Trend Oscillator, MACD, or RSI) will confirm the possible direction of the new trend.