Bitcoin (abbreviation: BTC[a] or XBT;[b] sign: ₿) is a decentralized digital currency. Bitcoin transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. The cryptocurrency was invented in 2008 by an unknown entity under the name Satoshi Nakamoto.[9] The currency began use in 2009,[10] when its implementation was released as open-source software.[7]: ch. 1  The word "bitcoin" was defined in a white paper published on October 31, 2008.[3][11] It is a compound of the words bit and coin.[12]