The term "front matter" refers to the preliminary pages of a book or a document, which typically includes the title page, copyright page, table of contents, and preface. Antonyms for "front matter" may include "back matter," which refers to the material found at the end of a book or document, such as the index, bibliography, and appendix; or "core content," which refers to the main body of the text that contains the substantive information or message. Another antonym for "front matter" could be "irrelevant material" or "fluff," as some readers may consider the preliminary pages to be less important or essential to the content of the text.