The term 'Stuff in the Back of the Book' refers to additional material that is included at the end of a book, such as appendices, glossaries, and indices. The crossword solution for this term is 'ADDENDA, ' which is a plural form of the Latin word 'ADDENDUM, ' meaning something added or to be added. ADDENDA are typically found at the end of a book and include supplementary information that was not included in the main text.