base 5 is a positional numeral system with five as its base. It uses 5 different digits for representing numbers. The digits for base 5 could be 0, 1, 2, 3, and 4.

base 4 is a positional numeral system with four as its base. It uses 4 different digits for representing numbers. The digits for base 4 could be 0, 1, 2, and 3.