Blockchain is a distributed, peer-to-peer ledger that is immutable, append-only, cryptographically-secure, and updateable only through agreement or consensus among peers.
Blockchain is a distributed and decentralized, peer to peer ledger system that is almost immutable and is secured cryptographically.
The data can only be appended to the blockchain but cannot be edited or deleted. Data once added to the blockchain is distributed and copied to all th peers in the distributed system and is stored permanently.
The transactions in a blockchain are verified and added by using different consensus algorithms like Proof of work and Proof of Stake