A ghost writer is a person who writes any form of text, including books or even music, that is accredited to the person he is writing for. They are often used by famous people such as celebrities, politicians, business executives and other high profile people in the public limelight to write memoirs, autobiographies, music or anything else they desire. Written work such as books can be either fiction or nonfiction.
Ghost writers do not have to write all the work; they may do the research and create a rough draft, and then leave the writing to the client. Or they may do a draft of the work, or just edit and fill in some more information after being given a draft.