Column XO is an indicator in Prashant Shah's book Trading The Markets The Point & Figure Way. It counts a number of Xs and Os in every column for the long period. Then, the result is divided by the number of columns which is set by length.
This indicator is designed to identify changes in volatility and works well with Wyckoff's Law of Cause and Effect. The longer the price spends in the consolidation, the more volatile and far-reaching should the expansion phase be.