His Private Key Never Touched the Internet -- He Still Lost $1.6 Million. Inside the Coldcard Weak-Key Exploit

A block is the basic unit of a blockchain — think of it as one page in the ledger. Each block packages a batch of transaction records, plus a timestamp and a fingerprint pointing to the previous block (the previous block's hash). Blocks link in order, head-to-tail by hash, forming the blockchain — which is where the name comes from.

The set of rules by which all nodes in a blockchain agree, without any central administrator, on what the next <a href="/en/glossary/blockchain-fundamentals/block/">Block</a> looks like and which transactions are valid. It's the core that lets a decentralized network operate securely and resist fraud; the two most common are <a href="/en/glossary/blockchain-fundamentals/proof-of-work/">Proof of Work</a> (PoW) and <a href="/en/glossary/blockchain-fundamentals/proof-of-stake/">Proof of Stake (PoS)</a>.