The basic definition of a is when two publishing houses publish the same edition of a book (or equivalent versions of an edition, for example, translated versions), simultaneously or near-simultaneously, usually in different countries. English and American editions may differ in spelling. Some examples:
The term "first trade edition," refers to the earliest edition of a book offered for sale to the general public in book stores. For example, 's 1906 novel was published in two variant forms. A "Sustainers' Edition", published by the Jungle Publishing Company, was sent to subscribers who had advanced funds to Sinclair. The first trade edition was published by to be sold in bookstores.
While the latter is of the utmost concern to the book collector and the bookseller when pricing a book within the current market, the former must be considered, if only slightly, when making a collectible book purchase with investment concerns. Since most librarians currently do not know how to correctly identify first editions of contemporary American picturebooks, it is problematic to query libraries/institutions using Worldcat to understand the population statistics for such books. Still, keep this in mind as the hobby matures. Eventually, libraries will house first edition collections of Caldecott Medal books, Seuss books, and the like, so querying Worldcat while not be as futile.
For the most part, the first edition of a book is more meaningful to the world of book collectors than it was to the publisher who printed it. That's because the first printing only represents a portion of the total number of copies of a book that the publisher hopes to sell. That first printing is just an installment on what they hope to be a long term investment in that book. The first printing of a book might contain a few thousand copies. As those copies are shipped out to bookstores and sold, publishers will start a second printing to meet consumer demand. Because most publishers aren't typically in the business of trading in rare and collectible books, they haven't necessarily had a strong reason for a unified and consistent way of identifying first editions.