Permissionless blockchains are open to anyone to use, you can even participate in their consensus mechanisms, give that you meet specific requirements, Bitcoin, Ethereum and BNB chain are all examples of permissionless blockchains, which are typically transparent and decentralized.
Permissioned Blockchains, on the other hand require invitations to join, they are typically used in private business settings and tailored for certain used cases. Power is restricted to a small group of validators who make most of the network decisions, Transparency can be limited, but network upgrade time and scalability are often greatly improved.
