A micrometre (American English: micrometer), symbol µm is an SI unit of length that is defined as one millionth of a metre (or 1 × 10-6 m). The letter µ is the Greek letter mu. The micron is an older name for the micrometre. The name micron, and its symbol µ, are frequently discouraged, but still used (especially in astronomy).
For a list of objects on the order of one to a 10 micrometres, see 1 E-6 m.