surreal number
A mathematical concept introduced by John Conway; used in combinatorial game theory and analysis. This is a technical term.
Surreal numbers form a system that includes not only real numbers but also infinitesimals and infinities.
From 超 (chō, 'super-') + 現実 (genjitsu, 'reality') + 数 (sū, 'number'), a calque of English 'surreal number'.