noun which may take the genitive case particle 'no'
on shelf; available in the library
Used in library contexts to indicate that a book is currently on the shelf and available for borrowing or consultation, as opposed to being checked out or missing.
その本は在架ですので、すぐに借りられます。
That book is on the shelf, so you can borrow it right away.
在架の資料は自由にご覧いただけます。
You may freely browse the materials that are on the shelf.