WordNet (r) 3.0 (2006):

irrational number
    n 1: a real number that cannot be expressed as a rational number
         [syn: irrational number, irrational]

The Free On-line Dictionary of Computing (30 December 2018):

irrational number

    A real number which is not a rational
   number, i.e. it is not the ratio of two integers.

   The decimal expansion of an irrational is infinite but does
   not end in an infinite repeating sequence of digits.

   Examples of irrational numbers are pi, e and the square
   root of two.

   (1995-04-12)