base 6 is a positional numeral system with six as its base. It uses 6 different digits for representing numbers. The digits for base 6 could be 0, 1, 2, 3, 4, and 5.
base 7 is a positional numeral system with seven as its base. It uses 7 different digits for representing numbers. The digits for base 7 could be 0, 1, 2, 3, 4, 5, and 6.