What is Absolute and Relative Permeability?

Absolute permeability and relative permeability are terms used in the context of materials that affect how magnetic fields interact with them. Absolute permeability (μ) is a measure of how easily a material allows the passage of magnetic lines of force. It is a property of the material itself and is measured in henries per meter (H/m). 

The higher the permeability, the easier it is for the magnetic field to pass through the material. Relative permeability (μr) is the ratio of the material's absolute permeability to the permeability of free space (μ₀). It is a dimensionless quantity. A relative permeability greater than 1 means the material is magnetically susceptible and enhances the magnetic field, while a relative permeability less than 1 indicates the material resists magnetic fields.