Blockchain is a decentralized technology that records transactions across multiple computers in a way that ensures security, transparency, and immutability of the data. Each block in the chain contains a cryptographic hash of the previous block, along with transaction data, and timestamp. Once recorded, the data in any block is non-tamperable without altering all subsequent blocks, making blockchain resistant to tampering and fraud. Blockchain technology is the backbone of cryptocurrencies like Bitcoin and Ethereum, but its applications extend beyond finance to supply chain management, voting systems, smart contracts, and more.