In general, a reference is something that refers or points to something else, or acts as a connection or a link between two things. The objects it links may be concrete, such as books or locations, or abstract, such as data, thoughts, or memories.
The term reference is used with different specialized meanings in a variety of fields, as follows:
In semantics, reference is generally construed as the relation between nouns or pronouns and objects that are named by them. Hence the word "John" refers to John; the word "it" refers to some previously specified object. The objects referred to are called the "referents" of the word. Sometimes the word-object relation is called "denotation" for clarity.
Reference is not in general the same as meaning, as words can often be meaningful without having a referent. Fictional and mythological names such as "Bo-Peep" and "Hercules" show that this is possible.
As Frege discovered, reference cannot be treated as identical with meaning: "Hesperos" (an ancient Greek name for the evening star) and "Phosphorus" (an ancient Greek name for the morning star) both refer to Venus, but the astronomical fact that '"Hesperos" is "Phosphorus"' can still be informative, even if when understand both "Hesperos" and "Phosphorus". This problem led Frege to distinguish between the sense of a word and its reference.
In computer science, references are datatypes which refer to an object elsewhere in memory, and are used to construct a wide variety of data structures such as linked lists. Most programming languages support some form of reference. See reference (computer science).
The C++ programming language has a specific type of reference also referred to as a reference; see reference (C Plus Plus).
A reference point is a location used to describe another one, by giving the relative position.
Similarly we have the concept of frame of reference (both in physics and figuratively), etc.
In a library, the word reference may refer to a dictionary, encyclopedia, or other reference work that contains many brief articles that cover a broad scope of knowledge in one book, or a set of books.
However, the word reference is also used to mean a book that cannot be taken from the room, or from the building.
Many of the books in the reference department of a library are reference works, but some are books that are simply too large or valuable to loan out.
Conversely, selected reference works may be shelved with other circulating books, and may be loaned out.
A reference may also be a text (not necessarily a reference text) that has been used in the creation of a piece of work such as an essay, report, or oration. Its primary purpose is to allow people who receive such work to examine the author's sources, either for validity, or simply to learn more about the subject. Such items are often listed at the end of an article or book in a Reference list
A reference can also be a person whose name is submitted by somebody seeking employment. Usually, the reference is a previous superior or has some distinguishable profession in government, clergy, or education that can professionally vouch for the submitting person's employability.