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A blockchain is a shared digital ledger nobody owns. Think of it as a notebook everyone can write to, but once something is recorded it is nearly impossible to erase. 📓

Most databases are centralized - one party controls everything, so one breach risks it all. Blockchain is decentralized: many owners, no single trusted authority.

A distributed ledger is a database with no central server. Every node holds an identical full copy, so if one is lost or corrupted, the rest keep the data safe and consistent.

A new transaction is grouped with others into a block, then broadcast to the whole network. Every participant verifies it before adding it to their own copy of the ledger.

Once verified, a block is appended to the chain, carrying a cryptographic link to the previous one. This forms an unbroken, chronological, tamper-proof record.

Blocks are linked by hashing - a unique fingerprint of the data. Each block embeds the previous block's hash, so changing any old block breaks every link after it.

Because each block is hashed into the next, an added block is virtually impossible to alter. This property is immutability: once it's in, it stays in.

With copies everywhere, how does everyone agree on the next block? Consensus mechanisms are the rules that settle it - like Bitcoin's Proof of Work.

Blockchain's big wins: transparency, strong security from cryptography and distribution, decentralization with no single point of failure, and fewer intermediaries.

Let's check your understanding of blockchain's core principles.

Recap: blockchain is a decentralized distributed ledger of cryptographically linked blocks, made immutable and agreed on through consensus. Next up: Ethereum.