The term "public domain" refers to a body of knowledge and creative works that are not protected by intellectual property laws such as copyright, trademark or patent. This means that anyone can use, modify, distribute or build upon these works without obtaining permission from the original owner or paying any royalties.
The public domain includes works that have expired their copyright protection period (usually 70 years after the author's death), as well as those that were never protected by intellectual property laws in the first place, such as government publications and certain scientific research. Additionally, creative works are placed into the public domain intentionally by their authors or rights holders who choose to relinquish their control over them.
In summary, the public domain is a vast collection of knowledge and artistic works that belong to the public at large and can be used freely for any purpose without fear of legal consequences.