Glossary
Block
A batch of transactions, ordered and timestamped, that extends a blockchain. Each block commits to the previous one via its hash.
A block is the unit of progress on a blockchain. It contains a header (with a timestamp, a Merkle root of the transactions, and the hash of the previous block) and a list of transactions that the network has agreed to include at this height.
Because every block embeds the previous block's hash, blocks form an append-only chain — change anything in an old block and every later hash diverges, instantly invalidating the chain.