Answer is Public Blockchain.
Bitcoin is the most ambitious kind of blockchain. Anyone can use bitcoin’s cryptographic keys, anyone can be a node and join the network, and anyone can become a miner to service the network and seek a reward. Miners can walk away from being a node, return if and when they feel like it, and get a full account of all network activity since they left.
Basically, anyone can read the chain, anyone can make legitimate changes and anyone can write a new block into the chain (as long as they follow the rules). Bitcoin is totally decentralized. It is also described as a ‘censor-proof’ blockchain.
For these reasons, it’s known by its widest description, a public blockchain. But, this is not the only way to build a blockchain.
Blockchains can be built that require permission to read the information on the blockchain, that limit the parties who can transact on the blockchain and that set who can serve the network by writing new blocks into the chain.
For example, Ripple runs a permissioned blockchain. The startup determines who may act as transaction validator on their network, and it has included CGI, MIT and Microsoft as transaction validators, while also building its own nodes in different locations around the world.