Liouville number

Etymology
Named after (1809–1882), a French mathematician.

Noun

 * 1)  An irrational number x with the property that, for every   n, there exist integers p and q with q > 1 and such that $$\textstyle 0< \left |x- \frac{p}{q} \right| < \frac{1}{q^{n}}. $$