A measurement of digital information storage or transmission, and a multiple of the unit "bit" using the International System of Units prefix.
The Zettabit is 10^21 bits, or 1,000,000,000,000,000,000,000 bits or 1000 Exabits. A Zettabit is equal to 125 Exabit.
Zettabits have no practical applications as of 2011.
Very similar to zebibits, which use a more exact prefix established by the International Electrotechnical Commission.