A satoshi is the smallest unit of Bitcoin currency. 1 satoshi = 0.00000001 BTC. satoshi is the namesake of the technical author and creator of Bitcoin, satoshi Nakamoto.
Example: If 1 BTC = 100,000 yen, 1 satoshi = 0.0001 JPY.
In the Bitcoin protocol, the amount issued is in satoshi units. Major APIs also often display in satoshi units, so it is important not to mistake the units / order of magnitude.
It is possible that the system will be able to handle units smaller than 1 satoshi in the future.
Payments of less than 546 satoshi are usually referred to as "dust" and are generally not relayed or mined.