These are special sub-accounts that are opened to handle specific expenditure items such as procurement, stationery, benefits, etc. If the sub-account amount is expended, no funds may be withdrawn from other sub-accounts to cover them in order to ensure compliance with the budget.
I'm not sure about the term "intermediary", but it at least explains it. The phrase in parentheses was not worded clearly.
Maybe "sub-account" will be sufficient. Any ideas from anyone else?