A number system defines how we represent numbers. It defines which digits we can use, and what value each position (place value) in a number has.
The hexadecimal number system is the Base 16 number system. It is a number system that only uses 16 digits (0 1 2 3 4 5 6 7 8 9 A B C D E F)
Number system that has 16 digits 1 - 9 and A - F.