Bollinger Bands wrap a moving average (usually 20-day) in two lines set a number of standard deviations above and below it (usually two). Because the bands are built from volatility, they widen when the market gets jumpy and squeeze together when it goes quiet. So the chart shows both the trend (the middle line) and how turbulent it's been (the band width).
How it's read
Price riding the upper band is often described as stretched to the upside, the lower band to the downside; a "squeeze" (very narrow bands) is watched as a calm that sometimes precedes a big move. But statistically, price touching a 2-sigma band is normal and frequent — a touch is not a signal, and the bands say nothing about direction.
Where the ideas connect
Two threads. The mean-reversion read (snap back from a band) is the same short-horizon tendency behind our Short-Term Mean Reversion. And the volatility in the bands is the input our Inverse-Volatility strategy uses directly — it weights calmer names more. Both use volatility as a measured quantity, not as a chart-touch trigger. See reading a backtest.
Educational material — not investment advice.