Coercivity is defined as the minimum value of magnetising intensity that is required to bring the material to its original state. In the case of a ferromagnetic substance, when the applied magnetic field is increased in the reverse direction, then at some point Hc the substance completely loses its magnetization. This point is known as coercivity.
The ability of the magnetic field remaining in the material even after removing the external source is known as Retentivity. It tells us about the magnetic strength of the material. Or in other words when the applied magnetic field is decreased to zero after meeting the saturation point of magnetization, then the remaining magnetization shown by the substance is known as retentivity.