Satoshi

The satoshi is named after Satoshi Nakamoto, Bitcoin's pseudonymous creator, although the unit's name is a community convention and does not appear as such in the original whitepaper. Being a whole-number unit, it avoids floating-point errors. Amounts, fees (often expressed in sat per vByte) and transaction outputs are handled as integers of satoshis. Informally people sometimes refer to milli-bitcoin or microbitcoin, but the atomic unit of consensus is the satoshi.

It is essential for granular pricing, for micropayments and for wallet development, where any balance, fee or amount calculation is done in satoshis. On the Lightning Network operations run in sats and even in millisatoshis off-chain, which is only possible because the satoshi provides a precise integer base for all the accounting.

The unit runs through the whole cluster. It is the measure of the subsidy each halving trims and of the fees paid when spending UTXOs. In addition, Ordinals, the basis of BRC-20, numbers individual satoshis to give them identity, something that only makes sense precisely because the satoshi is the protocol's atomic, indivisible unit.