the.com/irrational number

means A real number, like √2 or π, that cannot be written as a simple fraction of two whole numbers — its decimal digits run on forever without ever settling into a repeating pattern.

from From Latin 'irrationalis' — not able to be expressed as a ratio ('ratio' in Latin literally means 'reckoning' or 'ratio'). The concept traces to ancient Greek mathematics, where it reportedly caused real distress: the Pythagoreans, devoted to the belief that whole numbers and their ratios governed everything, discovered that the diagonal of a simple unit square (√2) could not be expressed as any such ratio. Legend holds that the discoverer was thrown overboard for revealing it — a vivid story that is almost certainly later embellishment rather than verified history, but it captures how unwelcome the idea once was.