One followed by 30 zeros

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Nonillion \No*nil"lion\, n. [L. nonus ninth + -illion, as in E. million.] According to the French and American notation, a thousand octillions, or a unit with thirty ciphers annexed; according to the English notation, a million octillions, or a unit with ...

Wiktionary Word definitions in Wiktionary
n. (context hyperbole English) An unspecified very large number. num. 1 (context US modern British & Australian, http://en.wikipedia.org/wiki/Long%20and%20short%20scales English) 10 30 . 2 (''dated British & Australian, http://en.wikipedia.org/wiki/Long%20and%20short%20scales'') ...