Terminology
Historically, the constant μ0 has had different names. In the 1987 IUPAP Red book, for example, this constant was still called permeability of vacuum. Another, now rather rare and obsolete, term is "magnetic permittivity of vacuum". See, for example, Servant et al. The term "vacuum permeability" (and variations thereof, such as "permeability of free space") remains very widespread. However, Standards Organizations have recently moved to magnetic constant as the preferred name for μ0, although the older name continues to be listed as a synonym.
The name "magnetic constant" is used by standards organizations in order to avoid use of the terms "permeability" and "vacuum", which have physical meanings. This change of preferred name has been made because μ0 is a defined value, and is not the result of experimental measurement (see below).
Read more about this topic: Vacuum Permeability