I think it's a mix of currency and digital resource. Nowadays anything can be faked, from art to money, to even large quantities of gold can be doctored. Something that cannot be faked is definitely a valuable resource, and can be used like money, but using the current market price.
Bitcoin difined as a currency, because it is now started to accept as a digital currency. But i think it can considered also as a commodity, because of the demmand in our market. Many brought it investor.