Non Permissioned System implies open to all.
Non Permissioned System has no Permissions or Access Control
Non Permissioned System is precisely what has made bitcoin so ground-breaking:
In ensuring that no one owns the network, you give it to everyone. That is one of the major reasons why people who use bitcoin trust it. They know a transaction, once executed, is effectively irreversible.
Non Permissioned System is contrary to Permissioned Systems