Overview:
Bollinger Bands are similar in comparison to moving average envelopes. Bollinger Bands are calculated using standard deviations instead of shifting bands by a fixed percentage.

Interpretation:
Bollinger Bands (as with most bands) can be imposed over an actual price or another indicator.
When prices raise above the upper band or fall below the lower band, a change in direction may occur when the price penetrates the band after a small reversal from the opposite direction.

Parameters:
str Source
int Periods
int Standard Deviations
int Moving Average Type