[jprete]

It's the base, as in "base and exponent", of the value of a digit position. If the lowest digit is marked digit zero, then each digit of a number contributes (digit x base^position) to the total value. E.g. 1567(base 10) = 7x10^0 + 6x10^1 + 5x10^2 + 1x10^3.