The paper note of local currencies are called currency. Currency is the representation of money. Currency has no value but its representation has the value. Just like the paper has no value but the amount it represents is the values. Bitcoin is a currency because it has digital representation and that is why it is called a digital currency. Bitcoin is a currency.  But bitcoin is not just a currency but also an asset. Bitcoin is a commodity. Bitcoin is subject to volatile. The price of bitcoin increase over time and may later decrease. Bitcoin has been a hedge against inflation in long term. Some people and organizations like Microstrategy and retail investors are holding it and expect more adoption and more people to buy it for its amrketcap and its price to continue to increase just like gold. Because of this bitcoin is also an investment.