Public Domain encompasses “all works that never had copyright protection and works that no longer have copyright protection” (Purdue University Copyright Office). All works published in the United States before 1923 are in the public domain. All works in the public domain are free for the public to use.
Some examples of public domain material include:
Keep in mind: works that are not protected by copyright may still be protected by other intellectual property laws like trademark and patents. See the video below for information about the difference between these intellectual property laws.