Preface

An introductory essay written by a different person is a foreword[contradictory] and precedes an author's preface.

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.

While the former source of the word could have preface meaning the same as prologue, the latter strongly implies an introduction written before the body of the book.

With this meaning of stated intention, British publishing up to at least the middle of the twentieth century distinguished between preface and introduction.