Character Groups (as opposed to Permissions Groups) are groups of characters.
They may have influence over KV calculations, as such you may buff or alter certain groups abilities etc.
Groups are also used to implement “choose one from” attributes on a character sheet - groups are used for far more than just groupings.
Common examples of attributes may be Race, Class, or Faction (automatically implemented if the Faction module is enabled).
For example, you may create classes called Human, Elf, Dwarf, Orc, etc etc, and set all of these of type 'Race', which would also be a character attribute. Each character would then choose a singular race group to fill this attribute.
Character groups have an “open” feature, if set these groups may be joined by anyone, if a group is not open the character must be manually added or sent an invite to the group/faction.
Generally most factions would be closed, and invites sent by faction leaders/admins. There may be open factions that anyone can join like “Commoner” or similar.
Groups that control attributes, such as Race, Class, etc, should have the selectable groups left 'open' - unless you mark the attribute as 'self modifiable' the user will not be able to change the attribute once the character is created. If you have admin races/classes (such as 'deity' or similar) those groups should not be open and will not be selectable by characters at creation time, they must be manually moved after creation by an admin or group leader.