Micrometre
The micrometre (micrometer in US spelling; symbol: μm) is a unit of length in the International System of Units (SI) equalling 10−6 metre (SI standard prefix "micro-" = 10−6); that is, one millionth of a metre (or one thousandth of a millimetre, 0.001 mm, or about 0.00004 inch). It is also known as the micron.