Hecto is a decimal unit prefix in the metric system denoting a factor of one hundred. It was adopted as a multiplier in 1795, and comes from the Greek ἑκατόν hekaton, meaning "hundred". In 19th century English it was sometimes spelled hecato, in line with a puristic opinion by Thomas Young Its unit symbol as an SI prefix in the International System of Units (SI) is the lower case letter h.
It is rarely used, except in certain specific applications:
hectopascal (hPa), in meteorology, for atmospheric pressure, the modern equivalent of the traditional millibar.
hectolitre (hl or hL), in agriculture, for liquids (notably wine and milk) and bulk commodities (e.g., grain).
hectogram (hg), in agronomy, for quantities of animal feed (hectogram/animal) and for measures of agricultural productivity (hectogram/hectare); also used in Italy abbreviated as etto, and in Canada, New Zealand and Sweden simply as 100 g, for retail sale of cold cuts and meat.
hectometre (hm), in radio astronomy, occasionally used to indicate a radio band by wavelength
hectare (ha, or 100 ares), in surveying, as a measure of land area equal to one square hectometre, 1 hm2 = 10,000 m2
