A number system refers to a set of symbols or digits used to represent different quantities or values. It helps us count, measure, and perform mathematical operations like addition, subtraction, multiplication, and division. The most common number system used today is the decimal system, consisting of digits 0 to 9. Other number systems include binary (0 and 1), octal (0 to 7), and hexadecimal (0 to 9 and A to F).