A micrometre (the American spelling is micrometer; symbol is µm) is a unit of length in the SI measurement system. It can also be called a micron. It is one millionth of a metre. A micrometre is often used as a measurement for small things like bacteria. Like the Angstrom it is used for radiation in or near the visible spectrum.

This short article about science can be made longer. You can help Wikipedia by adding to it.