A number that cannot be expressed as a fraction. Irrational numbers are infinite decimals.
Example 1: The square root of 3 is an example of an irrational number. It is impossible to express the square root of three as a fraction. When converted to decimal form, the square root of three is an infinite decimal.
The square root of three = 1.7320508...
Example 2: π is another example of an irrational number. π converted to decimal form is an infinite decimal.