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prefix used in forming large units of measure (e.g. terabyte), 1947, from Greek teras (genitive teratos) "marvel, monster."
tera- pref. One trillion (1012): terahertz.
A prefix that means:
One trillion (1012), as in terahertz, one trillion hertz.
240 (that is, 1,099,511,627,776), which is the power of two closest to a trillion, as in terabyte.