A public blockchain is a decentralized and open network that anyone can participate in and access. Public blockchains, such as Bitcoin and Ethereum, are designed to be transparent and permissionless, meaning that anyone can join the network, verify transactions, and mine new blocks. They rely on a consensus mechanism, such as proof-of-work or proof-of-stake, to validate transactions and maintain network security.

In contrast, a private blockchain is a permissioned network that is owned and controlled by a single entity or a group of entities. Private blockchains are designed to be more secure and scalable than public blockchains, and they can be customized to meet specific business or regulatory requirements. Participants in a private blockchain network typically need to be approved by the network owner, and access to the network is restricted to a defined group of participants.