English Vocabulary for Librarians: Cataloguing, Reference & Archives

The Dewey Decimal System (DDC) organises knowledge into ten broad numerical classes (000-999), each divided into further subcategories, and is most commonly used in public libraries and school libraries because it is relatively simple to browse. The Library of Congress Classification (LCC) uses a combination of letters and numbers (for example, "PR" for English literature) and offers much finer subject granularity, which is why it is the standard system in most academic and research libraries with large, specialised collections. Both systems assign each item a unique "call number" that tells patrons exactly where to find it on the shelf, but the underlying logic and level of detail differ significantly between the two.

A reference interview is a structured conversation between a librarian and a patron designed to clarify exactly what information the patron actually needs, which is often different from their initial question. For example, a patron might ask "Do you have any books on Napoleon?" and the librarian's reference interview questions — "Are you interested in his military campaigns, his rise to power, or his personal life?" — help narrow down a large, vague request into something the librarian can address precisely. This vocabulary and skill is taught explicitly in library science programmes because effective reference service depends on accurately understanding the patron's underlying information need, not just their literal words.

A call number is a unique combination of letters and numbers assigned to every item in a library's collection, indicating both its subject classification and its exact physical location on the shelves. Patrons use the call number, found in the library catalogue, to locate an item themselves by walking to the correct section ("the stacks") and following the shelving order, which typically runs left to right, top to bottom. Understanding how to read a call number is one of the first practical skills taught to new library patrons and staff, since it is the primary system connecting the digital catalogue record to the physical item on the shelf.

The circulating collection consists of materials patrons are allowed to check out and take home for a set loan period, such as most novels, biographies, and general non-fiction. The reference collection consists of materials that must remain in the library at all times, typically because they are consulted briefly rather than read cover to cover, are needed by many patrons throughout the day, or are too valuable or fragile to risk losing — examples include encyclopaedias, atlases, and certain legal or medical reference works. Librarians and patrons both use these terms to quickly communicate whether an item can be borrowed or must be used on-site.

Interlibrary loan (commonly abbreviated ILL) is a service through which a library borrows an item from another library — sometimes in a different city or country — on behalf of a patron whose home library does not own that particular item. Patrons typically request an ILL when they need a specific book, article, or document that a librarian's search of the local catalogue confirms is not available on-site, and the request is fulfilled through a shared network of participating libraries. ILL requests usually take longer to fulfil than a normal checkout, so English-language library policies typically inform patrons of estimated wait times ranging from a few days to a few weeks.

Weeding, also called deaccessioning, is the systematic process of removing outdated, damaged, rarely used, or duplicate items from a library's collection to keep it relevant, accurate, and physically manageable within the available shelf space. Librarians use specific criteria when weeding, often summarised by the acronym MUSTY (Misleading, Ugly, Superseded, Trivial, Your collection doesn't need it), to decide which items to withdraw. Weeding is a routine, necessary part of collection management English-speaking librarians perform regularly, distinct from archival preservation, which instead aims to keep and protect unique historical materials indefinitely.

A finding aid is a descriptive document created by an archivist that summarises the contents, structure, historical context, and organisation of an archival collection, helping researchers understand what materials exist without having to examine every individual item physically. Finding aids typically include a biographical or historical note about the person or organisation that created the records, a scope and content summary, and a detailed inventory of boxes or folders. This vocabulary is specific to archival work, distinct from a library catalogue record, because archival collections are usually unique, unpublished materials (letters, photographs, organisational records) that require more contextual description than a standard published book.

A librarian typically manages published, often multiple-copy materials (books, journals, digital resources) organised for broad public or institutional access, with responsibilities spanning cataloguing, reference services, and collection development. An archivist typically manages unique, unpublished, single-copy historical materials (personal papers, organisational records, photographs) organised around preserving provenance and original order rather than a subject classification system. While both professions share overlapping vocabulary and are often housed in the same institution, English-language job postings and professional associations treat them as related but distinct careers, each with its own graduate qualification path and professional vocabulary.

Open access refers to scholarly research, articles, and academic content made freely available online to any reader, without a subscription fee or paywall restricting access. This is contrasted with traditional subscription-based academic journals, which libraries must pay significant fees to provide patron access to. Librarians frequently use "open access" vocabulary when discussing collection budgets, advocating for equitable access to research, or helping patrons and researchers locate freely available alternatives to paywalled articles, and many universities now have "open access policies" requiring researchers to deposit copies of their published work in publicly accessible repositories.

OPAC stands for Online Public Access Catalogue — the specific searchable database that allows patrons to look up whether the library owns a particular book, journal, or resource, check its availability status, and place holds or renewals. It is a component of the library's broader Integrated Library System (ILS), the complete software platform that also manages circulation records, cataloguing, and staff administrative functions behind the scenes. A library's general website may include the OPAC alongside other unrelated content like event calendars, staff directories, and research guides, so "OPAC" specifically refers to the catalogue search function rather than the whole website.