ILL is an abbreviation for Inter Library Loan, a service for ordering books and documents from libraries of other universities if they are not available in Nagoya University Library. It is also called an interlibrary loan.
https://www.nul.nagoya-u.ac.jp/guide/ILL_guide_e.html
* If the material you are looking for is not in the library on your campus, you can order a copy of the document or the actual book from another library.