Blockchains are accessed and built in different ways. Some blockchains allow anybody to participate in the networks with no restriction just like bitcoin blockchain where anyone can be a full node miner or partnering miner. On bitcoin blockchain, any individual can just keep a log of bitcoin transactions. Blockchains which are similar in functionalities to that of bitcoin blockchain are referred to as permissionless, open and transparent blockchains.
There are some blockchains in which their access layer are controlled by some specific individuals although they are not fully open or private. These blockchains are referred to as permissioned blockchains.