英汉词典

1. （书的）序言，前言，绪论
    A preface is an introduction at the beginning of a book, which explains what the book is about or why it was written.

2. 以…为开端；以…作为开场白
    If you preface an action or speech with something else, you do or say this other thing first.

preface

    e.g. I will preface what I am going to say with a few lines from Shakespeare...
           进入正题之前，我先引用莎士比亚的几句诗作为开场白。
    e.g. The president prefaced his remarks by saying he has supported unemployment benefits all along.
           总统在发表讲话前说他一直以来都支持发放失业津贴。