A Permissionless Blockchain is a blockchain, in which there are no restrictions on identities of transaction processors (i.e., users that are eligible to create blocks of transactions).

A Public Blockchain is a blockchain, in which there are no restrictions on reading blockchain data and submitting transactions for inclusion into the blockchain.

A Private Blockchain is a blockchain, in which direct access to reading blockchain data is allowed but submitting transactions into the blocks is limited to a predefined list of entities.

A Permissioned Blockchain is a blockchain, in which transaction processing is performed by a predefined list of subjects with known identities.