Block

A block is a batch of transactions that is added to a blockchain in one go. Each block has two parts: a header and a body. The body lists the transactions. The header contains summary data, including the hash of the previous block, a timestamp, a single hash (the Merkle root) that summarises all transactions in the block, and, on proof-of-work chains, the difficulty target and the nonce.

Because each header includes the previous block's hash, blocks form a chain stretching back to the very first one, the genesis block. The position of a block in that chain is called its block height.

Different networks produce blocks at different speeds. Bitcoin targets one block about every 10 minutes, with a limit of 4 million weight units per block since SegWit. Ethereum produces a block every 12 seconds. Faster blocks mean quicker confirmations but can make it harder for ordinary computers to keep up.