Source : WordNet®

quintillion
     n : the number that is represented as a one followed by 18 zeros

Source : Free On-Line Dictionary of Computing

quintillion
     
        10^30 in Europe (this is called a {nonillion} in the United
        States and Canada).
     
        10^18 in the United States and Canada (this is called a
        trillion in Europe).
     
        [Collins dictionary].