BTC is basically a virtual currency. It has no definate value, but can be exchanged for online payments and paypal.
same for gold and silver and other things. they too has no value. it is because of supply and demand that makes them valueable. so right now, bitcoin is limited but becuz of no much demand for it, it is still largely unknown to the world. so if btc can be made as another mode of payment commonly throughout, there will be huge demand for it.