Creative Commons licenses are one of the most widely used open content licenses.

Open content is content that is openly accessible, usable, editable, and distributable by anyone for any purpose, even commercially. Open content is licensed with an open license that authorizes use of the content as described above.

When someone creates something (like a picture or book), they can open it for the use of others. This means that other people are allowed to copy it and change it if they want. Something that is open content may be free of charge, but it does not have to be.