Who knows what it means [?] ...there is no exact definition.
It's all part of Apple's attempt to shield users from Unix permissions (which were further convoluted by ACLs since Leopard... well, Tiger really).
So, the answer lies on the command line... because I'll bet there are probably thousands of different possible combinations which Finder will simply display as being "custom". [ACLs actually raise that number into the tens-of-thousands, but some permutations are far less likely than others.]
List some of those items you named using:
ls -led /path/to/item
...and that's the only way to see what's actually going on.
Or, maybe a GUI tool like BatChmod or Sandbox might work. [i'm not sure if BatChmod shows ACLs though.]
