written or said at the beginning of something as an introduction to what follows 序言的；引导的；介绍的 introductory chapters/paragraphs/remarks 序篇；引言段；开场白
intended as an introduction to a subject or an activity for people who have never done it before 入门的；初步的 introductory courses/lectures 基础课程／讲座 The booklist at the end of the chapter contains some introductory reading on the subject. 章节末尾的书单列出了一些有关该主题的导读材料。
offered for a short time only, when a product is first on sale （新产品）试销的
Word Originlate Middle English (as a noun denoting an introductory text): from late Latin introductorius, from Latin introducere, from intro- ‘to the inside’ + ducere ‘to lead’.