Micro sign (µ, μ) is the Unicode character U+00B5.  It serves as a symbol for the SI prefix "micro"; it is the only non-Latin character used for an SI prefix.  Micro sign is derived from the small Greek letter mu (μ), The two may or may not look the same, depending on the font. The HTML representation for it is µ (whereas mu is represented as μ).

Many people think that the distinction between the "micro sign" and the "Greek letter mu" is artificial and meaningless.