chapter. chapters include. sample chapter.

In the book section https://glorian.org/books different books have different headings for the chapters. I assumed I knew the difference but now am wondering can you clarify.

chapter: https://glorian.org/books/the-mystery-of-the-golden-flower

sample chapters: https://glorian.org/books/the-major-mysteries

chapters include: https://glorian.org/books/beyond-death