A **number** is a mathematical object used to count, label, and measure. In mathematics, the definition of number has been extended over the years to include such numbers as zero, negative numbers, rational numbers, irrational numbers, and complex numbers.

Mathematical operations are certain procedures that take one or more numbers as input and produce a number as output. Unary operations take a single input number and produce a single output number. For example, the successor operation adds one to an integer, thus the successor of 4 is 5. Binary operations take two input numbers and produce a single output number. Examples of binary operations include addition, subtraction, multiplication, division, and exponentiation. The study of numerical operations is called arithmetic.

A notational symbol that represents a number is called a numeral. In addition to their use in counting and measuring, numerals are often used for labels (telephone numbers), for ordering (serial numbers), and for codes (e.g., ISBNs).

In common use, the word *number* can mean the abstract object, the symbol, or the word for the number.

Read more about Number: Classification of Numbers, Numerals

### Famous quotes containing the word number:

“I believe if we introduced the Lord’s Prayer here, senators would propose a large *number* of amendments to it.”

—Henry Wilson (1812–1875)

“As equality increases, so does the *number* of people struggling for predominance.”

—Mason Cooley (b. 1927)

“As Jerome expanded, its chances for the title, “the toughest little town in the West,” increased and when it was incorporated in 1899 the citizens were able to support the claim by pointing to the *number* of thick stone shutters on the fronts of all saloons, gambling halls, and other places of business for protection against gunfire.”

—Administration in the State of Ariz, U.S. public relief program (1935-1943)