# Real number

In mathematics, a **real number** is almost any number you would use in real life. Real numbers include whole numbers (such as 1, 2, 3), rational decimal numbers (32.3), irrational numbers (π), and negative numbers (-4). They are called "real" to differentiate them from "imaginary" (or "complex") numbers, which include a component multiplied by **i**, the square root of -1. Some real numbers can be difficult to use in computers, which must represent long or nonterminating numbers in a finite number of bits. As a result, some real numbers may be approximated, or rounded, to create a finite, floating-point representation.

For more information, see Real numbers at *Math is Fun!* and Oracle: What every computer scientist should know about floating-point arithmetic.