In general, a work is considered to be in the public domain if there is no legal restriction for its use by the public.

Black’s Law Dictionary defines the public domain as “[t]he universe of inventions and creative works that are not protected by intellectual-property rights and are therefore available for anyone to use without charge.  When copyright, trademark, patent, or trade-secret rights are lost or expire, the intellectual property they had protected becomes part of the public domain and can be appropriated by anyone without liability for infringement.”

The public domain has been defined in the field of copyright and related rights as “the scope of those works and objects of related rights that can be used and exploited by everyone without authorization, and without the obligation to pay remuneration to the owners of copyright and related rights concerned – as a rule because of the expiry of their term of protection, or due to the absence of an international treaty ensuring protection for them in the given country.”

In general, the public domain in relation to patent law consists of knowledge, ideas and innovations over which no person or organization has any proprietary rights.  Knowledge, ideas and innovations are in the public domain if there are no legal restrictions of use (varying in different legislations and forming, therefore, different public domains), after expiration of patents (regularly 20 years), in consequence of non-renewal, after revocation and after invalidation of patents.

The role, contours and boundaries of the “public domain” are under active discussion in several forums, including in WIPO and the IGC.  The “Note on Meanings of the Term ‘Public Domain’ in the Intellectual Property System, with Special Reference to the Protection of Traditional Knowledge and Traditional Cultural Expressions/Expressions of Folklore” discusses the meanings of the term “public domain” in relation to traditional knowledge and traditional cultural expressions further.