satoshi
A satoshi is the smallest unit of bitcoin. One bitcoin equals 100 million satoshis. The unit is named after Bitcoin's pseudonymous creator, Satoshi Nakamoto, and makes it practical to transact in very small amounts.
Bitcoin is divisible. One bitcoin can be split into 100,000,000 smaller units, each called a satoshi, commonly shortened to sat. This level of divisibility was a deliberate design choice. When Satoshi Nakamoto created Bitcoin, the protocol was built to handle transactions far smaller than one full coin, anticipating that the value of a single bitcoin might one day be very high. At a price of 100,000 USD per bitcoin, one satoshi is worth 0.001 USD, or one tenth of a cent. At higher prices, even a single satoshi carries real economic value.
The satoshi is important for two practical reasons. First, it allows Bitcoin to scale as a unit of account even as its price rises. You do not need to own a whole bitcoin to participate in the network. Buying, spending, or saving 10,000 satoshis is as valid as transacting in whole coins. Many Lightning Network payments are denominated in satoshis, enabling micropayments of fractions of a cent with near-zero fees. Second, divisibility ensures that Bitcoin remains usable for everyday transactions regardless of price.
The name honors the pseudonymous creator of Bitcoin, Satoshi Nakamoto, whose real identity has never been confirmed. Nakamoto published the Bitcoin whitepaper in October 2008, launched the network in January 2009, and disappeared from public communication in 2010. The decision to name the base unit after the creator is a community tribute, not an official designation from any protocol document. In addition to satoshi, other denominations exist: one millibitcoin equals 0.001 BTC, and one microbitcoin equals 0.000001 BTC, though satoshi remains by far the most widely used small unit.