Preface (noun)

1. A preliminary statement in a book, typically one explaining the scope and purpose of the work.
2. A short introduction to a play, film, or other work.
3. An introductory statement made before a speech, public statement, or other performance.

Origin:

From late latin praefatio, from latin praefari 'to speak beforehand'.

Examples:

1. The book's preface was written by the author's close friend.
2. She wrote a preface to the book, outlining her research methodology.
3. The ambassador's preface was a long and detailed explanation of the current situation.
4. In the preface of her novel, she thanked her family for their support.
5. The preface was followed by a table of contents that provided an overview of the book's chapters.