numeral
(US, modern British and Australian, short scale) A thousand trillion (logic: 1,000 × 1,000⁴): 1 followed by fifteen zeros, 10¹⁵.
(dated, UK, Australia, long scale) A million trillion (logic: 1,000,000⁴): 1 followed by twenty-four zeros, 10²⁴.
noun
(figuratively, slang, hyperbolic) Any very large number, exceeding normal description.