Bitcoin is a peer-to-peer cryptocurrency based on a Proof-of-Work consensus mechanism and a decentralized ledger called a blockchain. Satoshi Nakamoto announced Bitcoin on October 31, 2008 and the network launched on January 3, 2009.
Bitcoin has a limited supply of 21 million bitcoin and a fixed emission schedule. Every four years, Bitcoin’s inflation rate is cut in half, and it will eventually be reduced to zero. This trait makes Bitcoin unique among currencies; the supply of all other currencies is growing constantly, unpredictably, and boundlessly.
Bitcoin also has no central controller. Instead of a single database which provides data to users, all users maintain identical copies of the database, called the blockchain. This blockchain records all transactions made on the Bitcoin network, allowing users to independently verify their balances and transaction history. Bitcoin’s blockchain is append-only, meaning new blocks can be added but old blocks cannot be removed or altered.
Since Bitcoin is both a protocol and a currency, the way it is capitalized depends on the context. Bitcoin with a capital B is used to refer to the network and the asset class, while bitcoin with a lowercase b is used to refer to the coin, which is transferred in Bitcoin transactions and has a market price.