Magnetic permeability is the ability of the material to allow the passage of magnetic lines of force through it.
Relative permeability μr of a material is defined as the ratio of the number of magnetic lines of force per unit area B inside the material to the number of lines of force per unit area in vacuum B0 produced by the same magnetizing field.
so, Relative permeability μr = B/B0
μr = μH/μ0H = μ/μ0
(since μr is the ratio of two identical quantities, it has no unit.)
The magnetic permeability of the medium, μ = μ0 μr where μ0 is the permeability of free space.
Magnetic permeability μ of a medium is also defined as the ratio of magnetic induction B inside the medium to the magnetizing field H inside the same medium.
so, μ = B/H