Public domain

Works in the public domain are those whose intellectual property rights have expired, have been forfeited, or are inapplicable. Examples include the works of Shakespeare and Beethoven, The King James Bible, most of the early silent films, the formulae of Newtonian physics, and the patents on powered flight. The term is not normally applied to situations where the creator of a work retains residual rights, in which case use of the work is referred to as "under license" or "with permission".

In informal usage, the public domain consists of works that are publicly available; while according to the formal definition, it consists of works that are unavailable for private ownership or are available for public use. As rights are country-based and vary, a work may be subject to rights in one country and not in another. Some rights depend on registrations with a country-by-country basis, and the absence of registration in a particular country, if required, implies public domain status in that country.

Public Domain is one of the traditional safety valves in copyright law.

http://en.wikipedia.org/wiki/Public_domain