A copyright status indicating that a work is not protected by intellectual property rights and can be used freely by anyone, for any purpose, without permission or attribution.
Works enter the public domain in several ways: copyright expires (typically 70 years after the author's death in Canada), the creator explicitly dedicates the work to the public domain, or the work was never eligible for copyright protection (such as government works in some jurisdictions).
Public domain is not the same as open licence. An open licence grants specific permissions while retaining copyright. Public domain means there is no copyright to restrict use at all.
Example: Historical census records from the 1920s are in the public domain in Canada. Anyone can reproduce, republish, or build products from them without seeking permission or paying fees. A dataset published under a Creative Commons CC0 dedication is also effectively in the public domain.
When working with data, always check whether a dataset is truly in the public domain or whether it is licensed under terms that require attribution or restrict commercial use.