TREXRC,
You are talking about a grounding wire.
A GFCI, as said above, is a ground fault circuit interruptor. They are elecrical outlets designe to trip a breaker if there is a short circuit, and can save your live. They can be a bit finnicky, tripping when you don't want them to, but the added safety is worth it.
You should have one in your bathroom already, and have the little red reset button in them, usually.
You can get them at hardware stores, or electrical supply. But unless you are handy with electricty, I'd call an elcetrician and have him install one for you.