peta-
In units of measurement, a factor of 1015.
[Adapted from penta-, five, on the pattern of other SI (Système International) multiples (see the entry Words for multiples).]
The prefix appears most often in measures of computer data, such as petabyte; outside this field it is rare, though petagram (a multiple of a thousand million metric tonnes) sometimes appears in discussions of the global carbon cycle.
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