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:''This article is about a kind of publication. Reference work may also refer to the work that librarians perform at a library reference desk.''
A 'reference work' is a compendium of information, usually of a specific type, compiled in a book for ease of reference. That is, the information is intended to be quickly found when needed. Reference works are usually ''referred'' to for particular pieces of information, rather than read cover to cover. The writing style used in these works is informative; the authors avoid use of the first person, and emphasize facts. Indexes are commonly provided in many types of reference work. Updated editions are published as needed, in some cases annually.
In comparison, a 'reference book' or reference-only book in a library is one that may only be used in the library and not borrowed from the library. Many such books are reference works (in the first sense) which are usually used only briefly or photocopied from, and therefore do not need to be borrowed. Keeping them in the library assures that they will always be available for use on demand. Other reference-only books are ones that are too valuable to permit borrowers to take them out. Reference-only items may be shelved in a reference collection located separately from circulating items or individual reference-only items may be shelved among items available for borrowing.
Examples of reference works:

★ Almanac - a tabulation of information in specific fields, often by date

★ Atlas - a set of maps, often of geographical locations

★ Book by category - books listed in their category

★ Citation index - lists which publications cite other publications

★ Concordance - a list of every word in a book, and where it is used in that book

★ Dictionary or Lexicon (the latter generally provides more grammatical analysis) - an alphabetical listing of words and their definitions

★ Directory - a list of references, used for ease of locating their subject

★ Encyclopedia - a comprehensive compendium

★ Gazetteer - a geographical dictionary

★ Handbook - a manual which summarizes a subject

★ Mathematical tables - a tabulation of mathematical results

★ Periodical index - a list of topics for a periodical publication, organized by date

★ Scientific tables - a tabulation of scientific results

★ Thesaurus - a list of words with similar, related, or opposite meanings