Base n is the number of unique digits (including zero) that a positional numeral system uses to represent numbers, e.g. Base 10 (decimal) uses 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 in each place value position; base 2 (binary) uses just 0 and 1; base 60 (sexagesimal, as used in ancient mesopotamia) uses all the numbers from 0 to 59; etc.