What is the meaning of a permissioned blockchain? I know it is a private blockchain, but why is it called permissioned?
As I understand, you can compare it to a system with users having permission levels.
If it just a private blockchain, if someone knows the details about the network (bootnode, genisis file etc) he can join the network and run a full node with all permissions (participate in the consensus , auditing etc.)
But when it's a permissioned blockchain, some actions are limited to certain participants .
You may refer this blog post.
In a permissioned blockchain there are restrictions on who can participate (ie. users need 'permission' to join the network). It is generally opposed to a 'public' blockchain where anyone can participate.
This gets rid of the need for 'Byzantine fault tolerance' as each of the possible 'miners' are known in advance.