A generic word for a very large number. The term has no well-defined mathematical meaning. Conway and Guy define the nth zillion as 10^(3n + 3) in the American system (million = 10^6, billion = 10^9, trillion = 10^12, ...) and 10^(6n) in the British system (million = 10^6, billion = 10^12, trillion = 10^18, ...). Conway and Guy also define the words n-plex and n-minex for 10^n and 10^(-n), respectively.