The public domain includes every creative work that is no longer protected by a copyright, trademark, or patent. Creative works that are no longer protected are owned by the general public rather than the original creator. As such, the work is free to be copied, performed, or otherwise used by anyone.
As stated on the Stanford University Libraries site, creative works most commonly become public domain in the four following ways: (1) the copyright expires, (2) failure to properly renew a copyright, (3) the work is placed in the public domain deliberately by the copyright owner, and (4) the work was not of a type that can be protected by copyright. Further, certain transformative uses of the creative work can result in a new copyright owned by the one who created it. That being said, only the aspect of the use that is transformative can be copyrighted, not the public domain work itself. For example, all of Shakespeare’s works are in the public domain. While no one could claim a new copyright on any individual play, a new creator could copyright the specific arrangement of a collection of the plays. Further, new works based on the original works but with a creative new take can be copyrighted, such as the 1999 film “10 Things I Hate About You” based on “The Taming of the Shrew.”
[Last updated in July of 2020 by the Wex Definitions Team]