Learn English – The meaning of ‘shadow’ accounts

The use of inverted commas (aka quotation marks or quotes) around “shadow” strongly hints that this term is a euphemism, or a term which insiders /employees use among themselves. Technically, this type of drawing the reader's attention is called scared quotes.

shadow accounting
Accounting system in which two separate sets of financial books are kept for the purpose of finding a mistake.
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Wikipedia's page on shadow system suggests that a shadow account is secretive, hence the author's choice of inverted commas. It's his way of distancing himself from the meaning of the term.

Shadow System is a term used in information services for any application relied upon for business processes that is not under the jurisdiction of a centralized information systems department. That is, the information systems department did not create it, was not aware of it, and does not support it.