What µ means
It marks the micro prefix: one millionth of the following unit.
Write 5 µm for five micrometres; keep the prefix and unit together.
How is µ related to Greek μ?
They are separate characters with a shared measurement history.
In 1960, the International System of Units (SI) adopted µ for micro, one-millionth. Earlier, “micron” named the micrometre and µ stood alone for it; in 1967/68 the SI dropped that name and use because µ had become a prefix. Older Latin text systems included µ where Greek μ was unavailable. Unicode keeps µ for compatibility.
Don't confuse it with
1Questions people ask
1Why does µ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type µ
µ\00B5Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.