On the previous page we learned that OER are educational materials that are released under an open license or reside in the public domain.

A license basically says what you can and cannot do with a body of work. It gives you permission and restrictions. In education, the most common type of open licenses are the Creative Commons licenses. Without getting too deep into the history of Creative Commons, just know that a group of educators, philanthropists, technologists, legal scholars, investors and entrepreneurs came together in 2001 and created the first Creative Commons licenses. Yes, 15 years ago.

There are also certain bodies of work that reside in the public domain. Works in the public domain are those whose intellectual property rights have expired, have been forfeited, or are inapplicable--you don't have to ask permission to use them. Most works enter the public domain because of age. Here are some important dates to know about the works found in the public domain.
They were:

published before 1923 in the United States
published before 1964 without a renewed copyright
published before March 1, 1989 without a copyright or its protection was lost
the owner explicitly asked for the work to be given to the public domain
works of the U.S. Government and various other governments

The diagram below describes the differences between public domain, open license and copyright materials. Copyright materials have "fair use" guidelines and I promised you that we would not focus on copyright materials in this module. This is just to point out that these types of materials typically have more restrictions and a lot of times cost money!