A group of transactions that took place on a blockchain during a certain period of time. If a blockchain is thought of as a ledger, then a block is similar to one page from that book. It takes about 10 minutes to add a new block of transactions to the Bitcoin blockchain and less than 1 minute for the Ethereum blockchain. When a user's transaction is included in an added block on the blockchain, it is called a block confirmation.

A transaction from a user must receive multiple block acknowledgements (meaning it must be included in a series of blocks) before it is considered valid by the network. This ensures that multiple nodes have approved the inclusion of the transaction in each added block to the chain, increasing the likelihood that the transaction is correct.

The number of confirmations required depends on the digital currency.