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.
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 magazinesówith recent quotations by leading personalities on current topicsóhave also become commonplace.
The increase of written means of informal communication brought about by the Internet has produced the practice of using quotations as personal flags, as in one's own signature block. This is most commonly seen in email messages and Usenet posts, while it is almost never seen in blog posts. Quotations are also popular as a user's personal message, a line under the user's nickname in some Instant Messaging clients (and here they often go uncited). In all these cases, quotations are usually included to give a glimpse of the user's personality, to make a statement of their beliefs, or to spread views and ideas.
The sheer bulk of online quotations, combined with more efficient search engines, has effectively made the Internet the world's quotation storehouse, encompassing an unprecedented number of easily obtainable quotations. Though matters of accuracy still remain, features such as Amazon.com's Search Inside the Book and Google Book Search may serve to alleviate such concerns.