All amounts in the block chain are denominated in satoshi before being converted for display. The source code also uses satoshi when specifying an amount of bitcoin. When displaying an extremely small fraction of a bitcoin, as in a faucet, the amount is displayed in satoshi for readability.
As of July 2017, 1 US cent is worth approximately 430 satoshi.
On November 15, 2010, Ribuck proposed that the one hundredth of a bitcoin (0.01 BTC) be called a Satoshi. Four months later he instead suggested that the one hundred millionth unit be called an austrian or a satoshi. The name satoshi caught on, and was widely adopted thereafter.
Traditionally, the plural form has been simply satoshi, but the term satoshis is also popular. If the plural form were to follow the rules of Japanese grammar, it may be pronounced as satoshi, or satoshisa.
Satoshi is sometimes abbreviated to sat or s, although no symbol has been widely adopted.