General terms:
* Anonymous author: This is the most common and straightforward term.
* Uncredited author: This term specifically emphasizes the lack of credit.
* Pseudonymous author: This term is used when an author uses a pen name, but it doesn't necessarily mean they are uncredited.
* Ghostwriter: This term is usually reserved for authors who are hired to write for someone else, with the client taking the credit.
* Shadow writer: Similar to ghostwriter, but may be used in a more informal or less professional context.
Specific terms:
* "The author wishes to remain anonymous": This is a phrase often used in the acknowledgements section of a book.
* "As per the author's request, their name is not being disclosed": This is a similar phrase that emphasizes the author's decision to remain uncredited.
* "Written by [name of client]": This is a common way to credit a client for a piece of writing that they commissioned and may or may not have actually written.
The best term to use will depend on the specific situation and the information available about the author.