There is great confusion between the names of material used to sandwich the main portion of a book. Here are some brief guidelines to distinguish between them. It is based upon my own research. Apologies for any errors!
A prologue or epilogue is only used in fiction. All the rest are names for different types of material used in either fiction or non-fiction.
All these things are optional. None of them presume the need for any other.
Prologue. Only use a prologue in fiction. It comes BEFORE the actual beginning of the story to introduce characters or to explain past events or history that might need to be
explained, or to generally intrigue the reader. It's a great place to
provide information relevant to your story without have to go through
flashbacks or torturous dialogue in your first few chapters. Keep it short. Bear in mind many people skip it!
Epilogue. Only use an epilogue in fiction. It comes AFTER the story in order to provide some conclusion when the story leaves something hanging. Don't include plot spoilers in case someone reads it before the story!
Foreword. A foreword (NB NOT 'forward'), are words BEFORE the main text which are NOT written by the author. Someone else tell readers WHY they should read the book. This is the place for a guest celebrity or author to praise and introduce the book. It should make an emotional connection with the reader. A foreword should always be 'signed off' by someone other than the author.
Preface. A preface explains HOW the book came about. It is similar to a foreword, but it is written BY the book's author.
Introduction. An introduction does what it implies: it introduces WHAT follows as a concise overview for the reader.
Afterword. An afterword is similar to a foreword except that it comes AFTER the main work instead of before it. Another purpose is to respond to critical remarks made about a previous edition.
Postscript. Seldom used today, a postscript provides further information about the preceding work, perhaps containing brief information about a sequel or related material.
Footnotes. These are used at the foot of a page to amplify topics raised on the SAME page. They are linked to by reference numbers within the main text. Ensure they are on the correct page in the final printed work! If you need more than a couple on any given page, perhaps you should consider using End Notes instead. Too many footnotes become tiresome!
End Notes. These are used at the end of a book to amplify topics raised within the main body. They are normally linked to by reference numbers within the main text. They are less intrusive than footnotes, but are less likely to be read.
I hope you found this article helpful. Please visit my website, iankingsley.com to see what else I write!