noun which may take the genitive case particle 'no'
off-book; off-the-books
Describes transactions, assets, or activities not recorded in official accounts; often implies informal or hidden dealings.
The company was conducting off-the-books transactions.
Off-book assets were uncovered.
Compound of 帳簿 (account book, ledger) and 外 (outside, beyond), literally 'outside the ledger'.