A satoshi is one hundred millionth of a bitcoin. Each bitcoin can be divided into fractions up to 8 digits long. That means 1 bitcoin can be divided into a maximum of 100,000,000 subunits. Each 0.00000001 of a bitcoin is called a satoshi. This is the smallest possible fraction of a bitcoin. Satoshi is named for the original designer of Bitcoin, Satoshi Nakamoto.