Bitcoin (BTC)

Bitcoin is a decentralized digital money launched in January 2009 by the pseudonymous Satoshi Nakamoto. It runs on a public network where thousands of independent computers (nodes) verify every transaction against shared rules — most famously the fixed supply cap of 21 million coins. BTC is both the ticker and the largest unit; one BTC divides into 100 million satoshis.

What distinguishes Bitcoin from every currency before it is that nobody can change its supply schedule or reverse its transactions by decree — properties enforced by mathematics and distributed consensus rather than by an institution.