Number

A number is an abstract idea used in counting and measuring. A symbol which represents a number is called a numeral, but in common usage the word number is used for both the idea and the symbol. In addition to their use in counting and measuring, numerals are often used for labels (telephone numbers), for ordering (serial numbers), and for codes (ISBNs). In mathematics, the definition of a number has been extended to include new kinds of numbers, such as rational numbers, irrational numbers, zero, negative numbers, and complex numbers.

A process which converts inputted numbers into other numbers is called a mathematical operation. Examples include addition, subtraction, multiplication, division, and exponentiation. The study of mathematical operations is called arithmetic.

The branch of mathematics that studies abstract number systems such as groups, rings and fields is called abstract algebra.