Bitcoin (BTC) is a digital currency, often referred to as a cryptocurrency, created in 2009 by an unknown person or group using the pseudonym Satoshi Nakamoto. It was designed to be a decentralized, peer-to-peer electronic cash system, enabling users to make online payments directly to one another without needing an intermediary like a bank.

Key features of Bitcoin include:

1. Decentralization: Bitcoin is maintained by a network of computers, or "nodes," around the world. No central authority (like a government or bank) controls Bitcoin, which makes it immune to government interference or manipulation.

2. Blockchain Technology: Transactions are recorded on a public, decentralized ledger called the blockchain. Each "block" contains a group of transactions, and they are linked in a chain, ensuring transparency, security, and immutability.

3. Limited Supply: Bitcoin's total supply is capped at 21 million coins. This limited supply makes it deflationary by design, as opposed to fiat currencies, which can be printed in unlimited quantities by central banks.

4. Mining and Proof of Work: Bitcoin transactions are validated through a process called "mining." Miners use computational power to solve complex mathematical puzzles, which helps secure the network and process transactions. As a reward, miners receive newly minted Bitcoin.

5. Anonymity and Transparency: While Bitcoin transactions are public and can be viewed on the blockchain, the identities behind the transactions are anonymous, represented only by wallet addresses.

Bitcoin has inspired thousands of other cryptocurrencies and remains the most widely recognized and traded crypto asset globally. Its revolutionary nature has sparked widespread debate about the future of money, decentralized finance, and blockchain technology.