When a work (such as a textbook) is created, it is protected by copyright. However, when the creator assigns an open license to their work, they are allowing others to use their work in certain ways. For open educational resources, Creative Commons (CC) licenses are the most used type of license. There are six types of Creative Commons licenses that specify how someone can use a specific work. In addition, works in the public domain are freely available to use.
What is Creative Commons?
Creative Commons Aotearoa New Zealand. (2019) Creative Commons Kiwi. Retrieved from https://www.youtube.com/watch?v=F0hh1FuMMmA
If video is does not work, copy and paste the following link into your browser: https://creativecommons.org/about/videos/creative-commons-kiwi/
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Works in the public domain are the most open while copyrighted works are the least open. Works with one of the six Creative Commons licenses fall in between in terms of how open they are and how they can be used.
Image from Wikipedia: Creative Commons License