Actually I've tried to search the meaning of fiat (shame on me), this is as well to enlighten btc users who involves in daily activities:
Fiat currency is legal tender backed by a central government. It can take the form of physical dollars (for example paper Federal Reserve notes), or it can be represented electronically, such as with bank credit. The government controls the supply and you can pay your taxes with it.
Cryptocurrency is not legal tender and it is not backed by a central government or bank (it is decentralized and global). Its form is more like bank credit sans the bank (in that it is represented digitally, but not backed by a bank or government). An algorithm controls the supply and you cant pay your taxes with it (instead you have to pay taxes on it).
Reference: Crypto currency facts
Well I think as everybody though that this two (2) feature would co-exist one way or another as a point of improvement in the world systems' currency. The probability of gettin in their is the evolution of what we had right now. There were some instances that all of these would combine or would divide. Nobody knows specifically.