Deferred debits are a form of deferred expenses: amounts already paid or incurred that are held on the balance sheet as assets, with debit balances, until they are charged to expense in later periods as the benefit is used. The main entry explains the basic treatment.
Where the name comes from
The name describes the bookkeeping. In double-entry accounting, assets and expenses carry debit balances. A deferred debit is a debit that has been put off: rather than going straight to expense, it waits on the balance sheet. The matching term on the other side is deferred credits, which covers amounts received in advance, such as deferred revenue, that sit as liabilities until earned.
The phrase is most common in regulated industries. The uniform systems of accounts used by many US electricity and gas utilities group a range of items under a "deferred debits" heading, including costs that a regulator has allowed to be recovered from customers through future rates. Outside such settings, companies more often use the wording deferred charges or other assets.
Like all deferrals, deferred debits rely on judgement about future benefit. If the expected benefit or recovery no longer looks likely, the balance has to be written off to expense.