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