A Satoshi also known as a (SAT) is the smallest unit of Bitcoin - kind of like a penny, but way smaller. There are 100,000,000 Satoshis (SATS) in one Bitcoin.

1 Satoshi = 0.00000001 BTC

The name comes from Satoshi Nakamoto, the pseudonym used by the creator/creators or Bitcoin. Satoshis or SATS make it possible to break Bitcoin down into 100 million units.