The Concrete Encased Electrode, commonly known as a “UFER”, is used for grounding your building’s electrical system.  A piece of rebar is tied to the reinforcing rebar within the floor’s thickened edge perimeter known as a grade beam.  It then protrudes from the slab typically within the wall cavity so the electrician can attach the service grounding wire.  The reinforcing rebar acts as the grounding rod with much more ground contact; however, it is ineffective when foam is used under the slab in the case of a shallow frost foundation or fiberglass rebar is used in lieu of steel.  By the way, “UFER” is the last name of the gentleman that came up with this grounding system.