A blockchain can be both permissionless (like Bitcoin or Ethereum) or permissioned (like Hyperledger blockchain frameworks). A permissionless blockchain is also known as a public blockchain, because anyone can join the network. A permissioned blockchain, or private blockchain, requires pre-verification of the participating parties within the network, and these parties are usually known to each other.
Hyperledger
Hyperledger is an open source effort created to advance cross-industry blockchain technologies. Hosted by The Linux Foundation, it is a global collaboration of members from various industries and organizations. Hyperledger boasts a host of enterprise-ready solutions. Hyperledger is about communities of software developers building blockchain frameworks and platforms.
Hyperledger blockchains are generally permissioned blockchains, which means that the parties that join the network are authenticated and authorized to participate on the network. Hyperledger’s main goal is to create enterprise grade, open source, distributed ledger frameworks and code bases to support business use cases.
If you look at permissionless blockchains, like the Bitcoin blockchain or the Ethereum blockchain, anyone can join the network, as well as write and read transactions. The actors in the system are not known, which means there could be some malicious actors within the network.
Hyperledger reduces these security risks and ensures that only the parties that want to transact are the ones that are part of the transaction and, rather than displaying the record of the transactions to the whole network, they remain visible only to the parties involved. So, Hyperledger provides all the capabilities of the blockchain architecture - data privacy, information sharing, immutability, with a full stack of security protocols - all for the enterprise.