Which of the following is an example of an off-book fraud?

Skimming is an example of an off-book fraud because it involves the theft of cash before it is recorded in the accounting system. In skimming, an employee takes cash from a sale and fails to deposit it into the company's records, resulting in a loss that is not reflected in the financial statements. This type of fraud specifically avoids the books, making it particularly difficult to detect since there are no transactional records to review.

In contrast, other options such as ghost employee schemes, cash larceny, and billing schemes typically involve some level of recording within the company's financial systems, whether it's fraudulent payroll expenses, theft from recorded cash, or false invoicing. Thus, skimming stands out as a pure form of off-book fraud, as it directly impacts cash flow without ever being entered into the official accounting records.