A preface is an introduction to the main text of a book, when an author or critic can write directly to the reader. A preface often describes how a book came together, like a behind-the-scenes glimpse of the final product.
The preface is a place for extra context, thoughts, or even disclaimers about the text that follows. In his preface to Lyrical Ballads, the famous poet William Wordsworth wrote, “The majority of the following poems are to be considered as experiments.” In other words, “Don’t judge me too harshly!” Preface can also be used as a verb meaning "introduce." When you preface a statement with, “No offense but... ,” the person you’re talking to braces for criticism.