From Wikipedia:
"The public domain consists of all the creative work to which no exclusive intellectual property rights apply. Those rights may have expired,[1] been forfeited,[2] expressly waived, or may be inapplicable.[3]"
I would say a public domain work is even better than free since it more explicitly states that there's no copyright on the work released.
Here's an article I found on public domain and commercial rights.
https://askwonder.com/research/commercial-rights-license-sell-artwork-public-domain-z9x6wfrzkAll times are CEST. The time is now 21:06