A reference work is a book or periodical (or its electronic equivalent) to which one can refer for information. The information is intended to be found quickly when needed. Reference works are usually referred to for particular pieces of information, rather than read beginning to end. The writing style used in these works is informative; the authors avoid use of the first person, and emphasize facts. Many reference works are compiled by a team of contributors whose work is coordinated by one or more editors rather than by an individual author. Indices are commonly provided in many types of reference work. Updated editions are usually published as needed, in some cases annually (e.g. Whitaker's Almanack, Who's Who). Reference works include dictionaries, thesauruses, encyclopedias, almanacs, bibliographies, and catalogs (e.g. catalogs of libraries, museums or the works of individual artists). Many reference works are available in electronic form and can be obtained as application software, CD-ROMs, DVDs, or online through the Internet.
A reference work is useful to its users if they attribute some degree of trust.
In comparison, a reference book or reference-only book in a library is one that may only be used in the library and may not be borrowed from the library. Many such books are reference works (in the first sense), which are, usually, used briefly or photocopied from, and therefore, do not need to be borrowed. Keeping reference books in the library assures that they will always be available for use on demand. Some reference-only books 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. Some libraries consist entirely, or to a large extent, of books which may not be borrowed.
An electronic resource is a piece of information that is stored electronically, which is usually found on a computer, including information that is available on the internet. Libraries offer numerous types of electronic resources, such as subject research guides, indices, electronic books and texts, electronic journals, library catalogs, reference sources, statistical sources, sound recordings, and image databases.