Satoshis, often abbreviated to “sats”, are the atomic unit of Bitcoin, named after Bitcoin’s creator, Satoshi Nakamoto. A single Bitcoin represents 100 million satoshis (1 BTC = 100,000,000 sats). Thus, there will only ever be 21 million bitcoin, and there will only ever be 2.1 quadrillion sats.

In Bitcoin’s codebase, all values are actually denominated in satoshis, and the unit Bitcoin is only used by markets and those discussing Bitcoin.