Block

A block is the basic unit of a blockchain. It has two parts: a header with metadata such as a timestamp, the hash of the previous block and a summary of its contents, and a body with the list of transactions it confirms.

Blocks are produced at a roughly steady pace set by each protocol. Bitcoin targets one block about every 10 minutes, while Ethereum produces one every 12 seconds. The position of a block in the chain is called its block height, and each new block added on top of a transaction counts as one more confirmation.

Block size and block time limit how many transactions a network can process, which is why fees rise when demand exceeds the available space. The miner or validator that produces a block collects a reward plus the fees paid by the transactions inside it.