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 16 is a positional numeral system with sixteen as its base. It uses 16 different digits for representing numbers. The digits for base 16 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, and f.