Block
A batch of transactions written permanently to a blockchain, linked cryptographically to the block before it.
A block is a bundle of validated transactions plus metadata: a timestamp, a reference (hash) of the previous block, and the proof that the network agreed to add it. Chained together by those references, blocks form the blockchain — alter one old block and every later link visibly breaks.
Each chain has its own rhythm: Bitcoin adds a block roughly every 10 minutes; many newer networks add them in seconds. Block space is finite, which is why demand spikes push up fees — users are bidding for room in the next block.