some definition

Magnetising field/ Magnetic intensity

It is define as the ratio of magnetic field in free space to the absolute permeability of free space denote by H. It's S.I. unit is A/m.

Intensity of magnetisation

The magnetic dipole moment produce per unit volume is known as intensity of magnetisation. It is denote by I and unit is A/m.

Relative permeability

It is define as the ratio of magnetic field in medium to the magnetic field in free space.  "The relative permeability is also define as the ratio of absolute permeability in medium to the absolute permeability in free space.

Magnetic susceptibility

Magnetic susceptibility of substance is define as the ratio of intensity of magnetisation to the magnetic intensity. It is unitless and dimensionless quantity.