A bitcoin transaction is considered unconfirmed until it has been included in a block on the blockchain, at which point it has one confirmation. Each additional block is another confirmation.Confirmation means that a transaction has been processed by the network and is highly unlikely to be reversed. Transactions receive a confirmation when they are included in a block and for each subsequent block. Even a single confirmation can be considered secure for low value transactions, although for larger amounts like $1000 USD, it makes sense to wait for 6 confirmations or more. Each confirmation exponentially decreases the risk of a reversed transaction.