Bitcoin is a fiat currency, if you want to pretend it's a currency.
From Dictionary.com (bold added):
fi·at [fee-aht, -at; fahy-uht, -at] Show IPA
noun
1.
an authoritative decree, sanction, or order: a royal fiat. Synonyms: authorization, directive, ruling, mandate, diktat, ukase.
2.
a fixed form of words containing the word fiat, by which a person in authority gives sanction, or authorization.
3.
an arbitrary decree or pronouncement, especially by a person or group of persons having absolute authority to enforce it: The king ruled by fiat.