Benzene is a form of hydrocarbon of the arene group which consist of rings of Carbon atoms each with a single Hydrogen atom bonded to it. The atomic properties of carbon mean that each Carbon atom in these rings is missing one bond. This bond is exhibited in arene rings as a delocalised electron cloud around the whole ring, or as transient pi bonds which switch from atom to atom very quickly. Benzene rings do not (as the above writeups would mostly have you believe) always have a totally symetrical pattern to their rings, there are several kinds of Benzene which all act in a small and barely noticably different way when Halogenated or Sulphonated. The differences arise from differences in the π bonds created around the ring by the delocalised electron clouds, which can form several different shapes, the full ring being only one of them.