Micro (Greek letter μ (U+03BC) or the legacy symbol µ (U+00B5)) 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 is the Greek letter μ (mu). It is the only SI prefix which uses a character not from the Latin alphabet. "mc" is commonly used as a prefix when the character "μ" is not available; for example, "mcg" commonly denotes a microgram. This may be ambiguous in rare circumstances in that mcg could also be read as a micrigram, i.e. 10−14 g; however the prefix micri is not standard, nor widely known, and is considered obsolete. The letter u, instead of μ, is allowed by an ISO document. Examples Typical bacteria are 1 to 10 micrometres (1–10 µm) in diameter. Eukaryotic cells are typically 10 to 100 micrometres in diameter...