What is Permissioned Ledger (Permissioned Blockchain)?

A permissioned ledger or permissioned blockchain is a blockchain system that employs an additional security system that consists of an access control layer that allows only certain parties to make use of the network. This means that accessing the network is often prohibited unless the user possesses a specialized security key or password, meaning that certain tasks can be carried out only by specific network participants with pre-determined access. Because of this structure, permissioned ledgers are very different from public blockchain systems like the Bitcoin and Ethereum networks.