A periodical index is a systematic and organized bibliographic tool that provides access to information by listing and describing articles, essays, and other short works published in a regular sequence of periodicals or serials, often categorized by subject, author, and date.

A publication issued at stated, more or less regular, intervals.

"In the context of medical literature, 'periodicals' refer to serialized publications released at regular intervals, containing peer-reviewed articles, research studies, and other scientific communications, which serve as a crucial resource for continuous professional development and dissemination of medical knowledge."

Interlibrary Loans is a service that facilitates the borrowing and lending of library materials between different libraries to provide their patrons access to resources that may not be available in their own library's collection.

Publications in any medium issued in successive parts bearing numerical or chronological designations and intended to be continued indefinitely. (ALA Glossary of Library and Information Science, 1983, p203)