A blockchain is a decentralized, distributed digital ledger that securely records transactions across a network of computers (nodes). Instead of a central authority, this peer-to-peer (P2P) network collectively validates new transactions through a consensus mechanism (like Proof of Work or Proof of Stake). Once a batch of transactions is verified, it is grouped into a block, which is then cryptographically linked to the previous block using a unique hash, forming a chronological chain. This linking makes the data immutable and tamper-proof, as altering one block would require changing every subsequent block across the entire distributed network. This structure provides transparency, security, and traceability for digital assets and data, making it the foundational technology for cryptocurrencies and smart contracts.