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bookcrossing

n. 1 (context uncountable English) The practice of leaving a book in a public location to be found and read by others, who then do the same. 2 (context countable English) An instance of the practice. vb. (present participle of bookcross English)

Wikipedia
BookCrossing

BookCrossing (also BC, BCing or BXing) is defined as "the practice of leaving a book in a public place to be picked up and read by others, who then do likewise." The term is derived from bookcrossing.com, a free online book club which was founded to encourage the practice, aiming to "make the whole world a library."

The 'crossing' or exchanging of books may take any of a number of forms, including wild-releasing books in public, direct swaps with other members of the websites, or "book rings" in which books travel in a set order to participants who want to read a certain book. The community aspect of BookCrossing.com has grown and expanded in ways that were not expected at the outset, in the form of blog or forum discussions, mailing lists and annual conventions throughout the world.