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'''''Tera''''' is a [[Metric prefix|unit prefix]] in the [[Metric system|metric system]] denoting multiplication by one trillion, or 10<sup>12</sup> or {{gaps|1|000|000|000|000}} (one trillion short scale; one billion long scale). It has the symbol '''T'''. ''Tera'' is derived from the [[Social:Ancient Greek|Greek]] word {{lang|grc|τέρας}} {{lang|grc-Latn|teras}}, meaning "monster";<ref name="usma">{{cite web | url=https://usma.org/si-prefixes-and-their-etymologies | title=SI prefixes and their etymologies | publisher=US Metric Association | accessdate=2021-06-11 }}</ref> also it resembles {{lang|grc-Latn|tetra}}, meaning "four" but with the middle letter removed as it is the fourth power of 1000.<ref>C. Upward, G. Davidson, ''The History of English Spelling'', Wiley-Blackwell (2011)</ref> The unit prefix was confirmed for use in the [[International System of Units]] (SI) in 1960.

Examples of its use:
*[[Physics:Terahertz radiation|terahertz radiation]]: electromagnetic waves within the band of [[Physics:Frequency|frequencies]] from 0.3 to 3&nbsp;[[Hertz#SI prefixed forms of hertz|THz]]. Visible [[Physics:Light|light]] is around 500 THz.
*[[Terabit|terabit]] and [[Terabyte|terabyte]], units used in data storage. Tebi-, or 2<sup>40</sup> is the closest binary prefix being ≈9.95% greater than 10<sup>12</sup>.
*teragram: equal to 10<sup>9</sup> kg. The Great Pyramid of Giza has a mass of about 6 Tg.
*terasecond: approximately 31,558 years
*teralitre: equal to 10<sup>9</sup> m<sup>3</sup>. Lake Zurich contains about 4 TL of water.
*[[Terawatt|terawatt]]: used to measure total human energy consumption. In 2010 it was 16 TW (TJ/s).
*terametre: (= 1,000,000,000 [[Kilometre|km]]): Light travels 1.079 Tm in one hour.
*terajoule: equal to 10<sup>12</sup> [[Joule|J]] of energy, approximately 1/4 [[Physics:TNT equivalent|kiloton]] of TNT.

{{SI prefixes (infobox)}}

==See also==
* [[RKM code]]

==References==
{{reflist}}

[[Category:SI prefixes]]

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