In Calc, choose File - Properties - Statistics tab page and show Help. Description of "Formula group" item would be useful here, because - contrary to the other items - it is not clear what the term means.
This content should go into source/text/shared/01/01100400.xhp but I have no idea about where to find a decent definition for Formula Group.
07:53:53 - mikekaganski: ohallot: supposedly they are the same formula in contiguous cells in one column
Olivier Hallot committed a patch related to this issue.
It has been pushed to "master":
tdf#102259 formula groups at Statistics tab page