Interlibrary Loan
Interlibrary Loan is a service whereby a patron of one library can borrow books, DVDs, music, etc. and/or receive photocopies of documents that are owned by another library.
The user makes a request with their home library; which, acting as an intermediary, identifies libraries with the desired item, places the request, receives the item, makes it available to the user, as well as arranges for its return.
(Definition URL: https://en.wikipedia.org/wiki/Interlibrary_loan)