[1] By applying a public license to a work, provided that the licensees obey the terms and conditions of the license, copyright holders give permission for others to copy or change their work in ways that would otherwise infringe copyright law.
[4] According to the Open Knowledge Foundation, a public copyright license does not limit licensors either.
The Open Source Initiative keeps a similar list of OSI-approved software licenses.
Considering all cultural works, as in the Open Definition, the four freedoms summarizes the main differences: The "open licenses" preserve the main freedoms of CC0, but add some reasonable restriction.
This is achieved by a public domain waiver statement and a fall-back all-permissive license.
The Unlicense offers a public domain waiver text with a fall-back public domain-like license inspired by permissive licenses but without attribution.