Micro-

Micro (symbol µ) is a unit prefix in the metric system denoting a factor of 10−6 (one millionth). Confirmed in 1960, the prefix comes from the Greek μικρός (mikrós), meaning "small".

The symbol for the prefix comes from the Greek letter μ (mu). It is the only SI prefix which uses a character not from the Latin alphabet.

Examples:
 * The size of the influenza virus is about 0.8 to 1.2 micrometres.
 * Typical bacteria are 1 to 10 micrometres in diameter. Eukaryotic cells are typically 10 to 100 micrometres in diameter.

Symbol encoding in character sets
For historical reasons, there are two different characters in Unicode, which appear slightly different in some fonts, although most fonts use the same glyph. The micro sign (µ) is encoded in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1985), at  (Unicode 1.0, 1991). The Greek letter (μ) is encoded in the Greek range at. According to The Unicode Consortium, the Greek letter character is preferred, but implementations must recognize the micro sign as well.

In circumstances in which only the Latin alphabet is available, the prefix can (unofficially) be represented using the letter u as in um for µm, or uF for µF.

Other abbreviating conventions
In some health care institutions, house rules deprecate the standard symbol for microgram, "µg", in prescribing or chart recording, because of the risk of misdose via the misreading of poor handwriting. The two alternatives are to abbreviate as "mcg" or to write out "microgram" in full (see also List of abbreviations used in medical prescriptions). But this deprecation, focused on bedside misdose avoidance in contexts where handwriting is often present, does not extend to all health-care contexts and institutions (for example, some clinical laboratories' reports adhere to it, whereas others don't ), and in physical sciences academia, "µg" remains the sole official abbreviation.