Library · Crypto, word by word · The basics
What is a block?
A block is a batch of transactions added to a blockchain together. Each block contains a hash (a fingerprint) of the previous block, which is what links the blocks into a chain. Ethereum, for example, adds a block every 12 seconds.
What it means for you
Your payment is not recorded when you press send, only when it is included in a block, and each later block makes it harder to reverse. Changing any past block would change every hash after it, so the network rejects the altered history.
Sources: ethereum.org: Blocks, bitcoin.org: Vocabulary · checked 4 October 2026
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