Public Domain
A branch of both Copyright and Intellectual Property, the public domain most often includes works whose copyrights or Intellectual Property rights have expired, and are therefore not covered under Intellectual Property law, and may be freely used by the public. Additionally, authors may also dedicate their works to the public, providing a dedication which makes it clear that the work is intended to be used freely and without permission from the author. Works in the public domain, whether books (including audio books, eBooks, et. cetera) music, photos, or movies, may be used and reprinted without permission or written consent. Though a slightly tricky topic, understanding public domain is essential for nearly any profession, as well as in our daily lives. However, knowing what public domain means and is can be particularly useful for undergraduate and graduate students.
As an undergrad, even as a grad student, it is prudent to understand which materials are freely available for use in papers, projects, and presentations; and which books you might not have to purchase, because they have been made freely available through websites such as Project Gutenberg, an excellent example and collection of public domain works.