A diamagnet is a type of material that exhibits a weak form of magnetism. When exposed to a magnetic field, diamagnetic materials create an opposing magnetic field, causing them to be repelled by the magnet. This effect is generally very weak and is present in all materials, but it is most noticeable in substances like bismuth and copper. Diamagnetism occurs due to the motion of electrons within the atoms of the material. When a magnetic field is applied, the electron orbits adjust slightly, leading to a small magnetic field that opposes the external field. This property is utilized in applications such as levitating magnets and magnetic resonance imaging (MRI).