There are two situations:
1, written by the author himself, is called "preface", which mostly explains its content, writing reason, process, theme and characteristics;
The preface written by others is called "preface", which introduces and comments on the ideological content and artistic characteristics of the book.
Extended data
The difference between preface and introduction:
Because the preface and preface are placed at the beginning of the volume, they are all a general introduction to the content of the book or the purpose and process of writing. Many people think that preface is a kind of preface, but there is a big difference between them. From the extension of the two, the preface has a wide range of applications, which can be used in both literary works, such as the preface to Scream, and academic works, such as the preface to Ancient Chinese by Mr. Wang Li.
The introduction can only be used in academic works. Sometimes academic works can have both a preface and an introduction, with the preface in front and the introduction behind. They have different functions and perform their respective duties. For example, the first draft of the History of Contemporary Literature in China has a preface before the article and an introduction at the beginning.
Baidu encyclopedia-preface