A nonregular number, also called an infinite decimal (Havil 2003, p. 25), is a positive number that has an infinite decimal expansion. In contrast, a number that has a finite decimal representation such as is said to be regular.
Nonregular numbers include repeating decimals, irrational numbers, and transcendental numbers.
More things to try:
Weisstein, Eric W. "Nonregular Number." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/NonregularNumber.html
is said to be regular.
