A batch of transactions that have occured on a blockchain within a period of time. If a blockchain is thought of as a ledger book, a block is like one page from the book.
It takes about 10 minutes for a new block of transactions to be added to the Bitcoin blockchain and less than 1 minute for a new block to be added to the Ethereum blockchain. When a user's transaction is included in a block that is added to the blockchain, this is called a block confirmation.
A user's transaction must receive several block confirmations (meaning it must be included in a series of blocks) before it can be accepted by the network as valid. This ensures that multiple nodes have essentially signed off on the transaction being included in each block that was added to the chain, making it more likely that the transaction is correct.
On Coinbase, incoming transactions show up in your account almost instantly (within a few seconds) but will show as 'Pending' until there have been enough block confirmations.
The number of confirmations needed is based on the digital currency. To see the number of confirmations needed for a specific asset that Coinbase supports, please refer to our Asset Directory.
To learn more, visit our help center article: Why is my transaction "pending"?