Diamagnetism is a form of magnetism that is only exhibited by an object in the presence of an externally applied magnetic field. It is the result of changes in the orbital motion of electrons. Consider two electron orbitals; one rotating clockwise and the other counterclockwise. An external magnetic field into the page will make the centripetal force on an electron rotating clockwise increase, which increases its moment out of the page. That same field would make the centripetal force on an electron rotating counterclockwise decrease, decreasing its moment into the page. Both changes oppose the external magnetic field into the page. However, the induced magnetic moment is very small in most everyday materials. http://en.wikipedia.org/wiki/Diamagnetic

Hey Max. Think of diamagnetism as anti-magnetism. When a substance is placed in a strong magnetic field, it causes changes in the electrons "orbit"...producing diamagnetism. [Since electrons do not 'orbit' the nucleus, [I can explain] it is difficult to know what 'layman terms' is.] Anyway, The electrons in a diamagnetic material re-arrange their "orbits" slightly, creating small currents which oppose the external magnetic field, creating diamagnetism. The forces created by diamagnetism are extremely weak...millions of times smaller than the forces between common magnets made of iron. [Key here is] diamagnets 'repel'...and are also 'repelled'...by this strong magnetic field. Materials such as water, wood, plants, animals, diamonds, fingers, etc. are considered to be non-magnetic, however, they are very weakly diamagnetic. In carefully arranged situations, the influence of diamagnetic materials can produce levitation. We know Magnetic N repels Magnetic N. Levitation was attempted with magnets, however, in 1842 it was proved that it is impossible to 'stably' levitate any static array of "magnets"... However, it was discovered that the addition of diamagnetic materials helps stabilize the object, making such levitation possible. Later, very high diamagnetic materials, such as graphite or bismuth, were discovered to highly 'repel' the pull of the standard magnet field enough to levitate. There is the site [cut and paste] <www.exploratorium.edu/snacks/diamagnetism_www/index.html> that has clearer info and an experiment that you may enjoy.