Micro-

Micro- (µ) is a prefix in the SI and other systems of units denoting a factor of 10&minus;6 (one millionth). Confirmed in 1960, the prefix comes from the Greek μικρός (mikrós), meaning "small".

The symbol for it is the micro sign &micro;, the Greek letter mu (&mu;). For historical reasons, these are two different characters in Unicode, which appear slightly different in some fonts. The micro sign is encoded in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1985), at U+00B5 (Unicode 1.0, 1991). The Greek letter is encoded in the Greek range at U+03BC.

In circumstances where only the Latin alphabet is available, the prefix is sometimes represented using the letter u as in "um" for µm, or "uV" for µV. In some contexts, such as pharmacy, micrograms are often written mcg. Neither variant is standard.