Bitcoin is a digital currency (cryptocurrency) that allows people to send and receive money over the internet without a central authority like a bank. It was introduced in 2009 by a mysterious figure or group using the name Satoshi Nakamoto. Bitcoin runs on a technology called blockchain, which is a public, unchangeable ledger of transactions. Only 21 million bitcoins can ever exist, making it limited in supply. It's used for investment, online purchases, and as a store of value, often called "digital gold." While it offers freedom and privacy, it’s also known for price volatility and environmental concerns from mining.