In mathematical numeral systems, the radix or base is the number of unique digits, including zero, used to represent numbers in a positional numeral system. For example, for the decimal system (the most common system in use today) the radix is ten, because it uses the ten digits from 0 through 9. In any standard positional numeral system, the number x and its base y are conventionally written as (x)y, although for base ten the subscript is usually assumed and not written, as it is the most common way to express value. For example, (100)10 (in the decimal system) represents the number one hundred, while (100)2 (in the binary system with base 2) represents the number four. Radix is a Latin word for "root". Root can be considered a synonym for base in the arithmetical sense.