Blockchain is a distributed digital ledger technology that records transactions across multiple computers in a way that makes the data tamper-resistant and transparent. At its core, blockchain combines cryptography, consensus mechanisms, and peer-to-peer networks to create trustless systems where participants can transact without intermediaries. Understanding blockchain fundamentals—from how blocks link through cryptographic hashes to how networks reach consensus—is essential for anyone working with cryptocurrencies, smart contracts, or decentralized applications. The key insight: blockchain achieves security not through central authority but through mathematical proofs and network-wide verification.