Bitcoin is a worldwide cryptocurrency and digital payment system invented by an anonymous person under the name Satoshi Nakamoto with a group of people, also anonymous, who released it as open-source software in 2009. It is the first decentralized digital currency of which now includes over 5,800 alternative coins. 

The system is peer-to-peer, and transactions take place between users directly (we pay each other), without an intermediary (bank). These transactions are verified by network nodes and recorded in a publicly distributed ledger called a Blockchain.