Similar answer to lly, with an example or two.
I suggest "nested subaccounts" as in the examples below.
Nested sub-accounts are organized under sub-accounts.
The following graphic shows a possible organization with the master
account (level 0), two sub-accounts (level 1) and several nested
sub-accounts (levels 2 to 4).
Themes are inherited from the account level, so that you can have a master theme, and then a subaccount theme that works along with the master theme that is loaded from the account level.
I was hoping that cascading inheritance functionality was in place for
nested subaccounts as well; meaning that a subaccount would inherit
the theme from the account level, but then also its parent subaccount,
and then its own theme.
A subset of the structure I'm working with looks like this...
. University (main account)
. Zone (Online, Media Media, Organizations, etc)