A blockchain, which is a database that is distributed across a number of servers to make it nearly impossible to delete and forge, can be used to store a record of all transactions or, equivalently, to record the amount of money held in an account. This allows one account holder to transfer funds to another party by publishing a transaction on the blockchain, thus confirming a transfer of funds; once the recipient sees that transaction on the blockchain, he knows that the funds have been transferred. Some blockchains are public, allowing everyone to see every transaction, and some offer limited visibility. In either case, the distributed nature of the database makes it very secure.