A curve showing the relationship between the flux density (B) in a piece of magnetized material and the magnetizing force (H) needed to produce the flux density.

Each type of ferromagnetic material, material that contains iron and is magnetizable, has a different B-H curve.

Each B-H curve consists of the virgin magnetization curve, the curve of B and H, when the material is first magnetized, and the closed hysteresis loop that shows the effect of hysteresis, the magnetism that remains in the material.