micron, mikron 1. Also called micrometer, it is the millionth part of a meter. Symbol: μ, mu. 2. In chemistry, it is a colloidal particle whose diameter is between 0.2 and 10 microns. 3. In physics, it is a very small unit of pressure, equal to that exerted by a column of mercury 1μ high. The links on a microchain drive created by Sandi...