A Numeral System is a Mathematical system of writing used to represent Numbers.
Some numerical systems include....
The numeral system I've used mostly are Arabic Numerals (like most people who speak English).
I've also used Roman Numerals a bit, as they often are used on Clocks and Wrist Watches, and in Chemistry.
In my work in Computer Science and Software Engineering I've also used Hexadecimal and Binary Numerals quite a bit.