A private blockchain is a permissioned blockchain. Private blockchains work based on access controls which restrict the people who can participate in the network. There are one or more entities which control the network and this leads to reliance on third-parties to transact. In a private blockchain, only the entities participating in a transaction will have knowledge about it, whereas the others will not be able to access it. Hyperledger Fabric of Linux Foundation is a perfect example of a private blockchain.