What does Bollinger Bands mean?

Bollinger Bands wrap a stock's price between an upper and lower band; the bands widen when volatility rises and pinch tight when it drops.

Bollinger Bands wrap price between an upper and lower band set 2 standard deviations from a 20-day SMA. Bands widen when volatility rises and pinch tight when it drops — a 'squeeze' often precedes a big move.