What do we mean by bohr magnecton?

In atomic physics, the Bohr magneton (symbol ?_B) is a physical conatant and the natural unit for expressing an electron magnetic dipole moment. The Bohr magneton is defined in SI units by

From the classical expression for magnetic moment, m = IA, an expression for the magnetic moment from an electron in a circular orbit around a nucleus can be deduced. It is proportional to the angular moment of the electron. The effective current is

which can be rewritten as so that the magnetic moment is