"A ghostwriter is a person who is hired to author books, manuscripts, screenplays, speeches, articles, blog posts, stories, reports, whitepapers, or other texts that are officially credited to another person. Celebrities, executives, participants in timely news stories, and political leaders often hire ghostwriters to draft or edit autobiographies, memoirs, magazine articles, or other written material. In music, ghostwriters are often used to writing songs, lyrics and instrumental pieces. Screenplay authors can also use ghostwriters to either edit or rewrite their scripts to improve them."
In the film industry, as screenwriter William Goldman and others have repeatedly pointed out, everything about the writing process has to do with teamwork and collaboration. Why should the same principles not apply to book writing? Ghostwriters are also hired to write books for people who perhaps have a great story to tell, or an important message, but don't feel they have the time or, possibly, the appropriate skills to write the whole thing themselves. In these cases, the accredited 'author' of the book is the person who hires the ghostwriter, unless the book author wants to share some of the credit with the ghost, in which case the book may be subtitled "As told to ...", or the ghost may be named as a co-author or “editor” of the book, and this is usually listed somewhere in the acknowledgments.