Magnetic susceptibility is a measure of how much a material will become magnetized in an external magnetic field. It indicates the degree to which a material can be attracted or repelled by a magnet. Materials can be classified based on their susceptibility: ferromagnetic materials, like iron, have high susceptibility and are strongly attracted to magnets, while diamagnetic materials, like copper, have low susceptibility and are weakly repelled. The value of magnetic susceptibility is usually expressed as a dimensionless number. Positive values indicate that a material is paramagnetic, meaning it is weakly attracted to a magnetic field, while negative values indicate diamagnetism. Understanding magnetic susceptibility is important in fields like material science and electromagnetism.