The term, “public domain,” sometimes called the “intellectual commons,” is used to refer to the body of published work to which no intellectual property rights apply. The concept of the public domain has its basis in ancient Roman law, which defined four realms of nonexclusive property: the res nullius, things yet to be appropriated; the res communes, things that cannot be appropriated; the res publicae, things owned in common by the public; and the res universitatus, things for which the state had authorized ownership by some corporate body (Rose, 2003).
Today, the public domain is made up of works that were never copyrighted, either because they are ineligible for copyright, like government documents, or because the copyright notice was messed up in the years before copyright was affixed automatically upon publication, like the Cary Grant film, Charade (Pierce, 2007).
The public domain also includes works for which copyright was not renewed during the years 1923-1963, when renewal was required, and you can search for a work’s renewal notice to find out if it is already in the public domain. Most public domain works were published before 1925, and thus their terms have expired, but there are many other reasons that works may be public domain.
Works can also be intentionally dedicated to the public domain, as were the basic technologies of the World Wide Web, but it is usually a better idea to preserve your copyright and publish your work under a Creative Commons license that prevents others from taking your work, repackaging it and republishing it under their own copyright.