The call /usermanagement/groupcategories is used to identify the groups that belong to a particular kind of category.
You see below that each group category has its own categoryId and name.
If you need the corresponding page in the user interface you find it here
But be careful to make any changes here unless you know exactly how it works.
In the example below you will find 6 different levels in the group type Organization unit.
That means that you can add 6 levels to the user groups of the group type organisation unit.