Magnetic permeability is defined as the degree to which the magnetic lines of force can penetrate or permeate the material. It can also be defined as the ability of the material to permit the passage of magnetic lines of force through it.
As the magnetic induction is proportional to the magnetising field
B proportional H
or B = μH
where μ is called the permeability of the medium (material)
Reference: This article is referred from my book “electrical engineering materials” having ISBN: 978-81-272-5069-0.