A Bollinger Band is a technical analysis indicator that is defined by a set of trendlines plotted by two standard deviations and a Simple Moving Average(SMA). Both of these deviations are plotted above (positively) and below (negatively) the SMA of a cryptocurrency's price.
Bollinger Bands are copyrighted by its developer - John Bollinger, who is an accomplished technical trader. Bollinger Bands give investors a higher sense of market understanding and hence can be proved to be very useful.