Block

A block is the basic unit of a blockchain. It contains a list of transactions, a timestamp, a reference to the previous block, and other data such as the solution to a mining puzzle or the signatures of validators. Once a block is added, the transactions inside it are considered confirmed, and each later block adds another confirmation on top.

Blocks are produced at a rate set by the protocol. Bitcoin targets one block roughly every 10 minutes, with a size limit that allows a few thousand transactions. Ethereum produces a block every 12 seconds. Solana produces blocks in about 400 milliseconds. Faster blocks mean quicker confirmation but require more from the computers keeping up with the chain.

Each block has a height, which is its position in the chain counting from the genesis block at height zero. Block explorers such as mempool.space or Etherscan let anyone look up a block by height or hash and see every transaction it contains.