Every term is defined twice: once the way a filing would put it, and once the way somebody would explain it to you across a table. The second one is usually the one that sticks.
Showing 3 terms
A statistical measure of how widely a series is dispersed around its own average; Bollinger Bands sit two of them either side of a 20-day mean.
It is recomputed every session, which is why the bands widen when a stock turns volatile and contract when it goes quiet. Touching a band means statistically unusual, never expensive.
A moving average with bands placed a set number of standard deviations above and below.
They define what is statistically normal for this stock — not what is expensive.
A quantified measure of how far price has moved from its own recent average.
Two standard deviations below a 20-day mean is overextension. "It has fallen a lot" is not.