A preface is an introduction to a book written by the author of the book. An introductory essay written by a different person is a foreword and precedes an author's preface. The preface often closes with acknowledgements of those who assisted in the project. A preface is usually signed (and the date and place of writing often follow the typeset signature); a foreword by another person is always signed. Information essential to the main text is generally placed in a set of explanatory notes, or perhaps in an "Introduction" that may be paginated with Arabic numerals, rather than in the preface. The term preface can also mean any preliminary or introductory statement. It is sometimes abbreviated pref.