A quotation is the repetition of one expression as part of another one, particularly when the quoted expression is well-known or explicitly attributed by citation to its original source, and it is indicated by (punctuated with) quotation marks.
A quotation can also refer to the repeated use of units of any other form of expression, especially parts of artistic works: elements of a painting, scenes from a movie or sections from a musical composition.
Quotations are used for a variety of reasons: to illuminate the meaning or to support the arguments of the work in which it is being quoted, to provide direct information about the work being quoted (whether in order to discuss it, positively or negatively), to pay homage to the original work or author, to make the user of the quotation seem well-read, and/or to comply with copyright law. Quotations are also commonly printed as a means of inspiration and to invoke philosophical thoughts from the reader.
Famous quotations are frequently collected in books that are sometimes called quotation dictionaries or treasuries. Of these, Bartlett's Familiar Quotations, The Oxford Dictionary of Quotations, The Columbia Dictionary of Quotations, The Yale Book of Quotations and The Macmillan Book of Proverbs, Maxims, and Famous Phrases are considered among the most reliable and comprehensive sources. Diaries and calendars often include quotations for entertainment or inspirational purposes, and small, dedicated sections in newspapers and weekly magazines—with recent quotations by leading personalities on current topics—have also become commonplace.
Chiefly a text medium in the beginning, the World Wide Web gave rise to any number of personal quotation collections that continue to flourish, even though very few of them seem to facilitate accurate information or correct citation.