When I was trying to delete a decommissioned remote desktop server from Active Directory I received the following message:

Object %COMPUTERNAME% is a container and contains other objects. Are you sure you want to delete object %COMPUTERNAME% and the objects it contains? This operation could take a long time if  %COMPUTERNAME% contains a large number of objects.

To determine which sub-objects this message referred to, I opened Active Directory Users and Computers.

I then selected View > User, Groups, and Computers as Containers.

I found the computer object in question, and expanded the plus sign to the left of the object name.  The sub-object was named TermServLicensing. The server was also a remote desktop licensing server, but we didn’t need it anymore, so it’s safe to delete the computer object, along with its TermServLicensing sub-object.