What is 1,000,000,000,000,000,000,000 called

This number is 1 sextillion in the short scale system (American/modern international usage)—that's 1 followed by 21 zeros. In the long scale system (historical European), this same number (10^21) would be called 1 trilliard.

To provide context, even in astronomical scales, sextillion rarely appears. The estimated number of stars in the observable universe is roughly a few hundred billion to a trillion—vastly less than a sextillion. However, when counting much smaller things, you might approach sextillion: the number of grains of sand on all Earth's beaches is estimated around 7.5 quintillion to a few sextillion. In computing, theoretical calculations about possible states or combinations in complex systems might reach these magnitudes. However, scientists and mathematicians working with such large numbers invariably use scientific notation (10^21) rather than saying "sextillion." These named numbers exist in the systematic Latin-based convention but serve more as linguistic artifacts than practical tools for describing quantities anyone actually encounters in measurements or calculations.