Zetta (symbol Z) is a SI prefix in the SI system of units denoting 1021 or 1 000 000 000 000 000 000 000.
Adopted in 1991, it comes from the French sept, meaning seven, because it is equal to 10007.
There was a bogus SI prefix of the same value, Hepa, which was informally introduced a few years before the promulgation of Zetta. It apparently came from the Greek ἑπτά, hepta, seven.
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