A ghostwriter is a professional writer who is paid to write books, articles, stories, reports, or other texts that are officially credited to another person. wikipedia.org

A letter is a written message from one party to another containing information.

A short story is a work of fiction that is usually written in prose, often in narrative format. This format tends to be more pointed than longer works of fiction, such as novellas (in the 20th and 21st century sense) and novels.

Fiction writing is the composition of not factual texts. Fictional writing often is produced as a story meant to entertain or convey an author's point of view.