Bitcoins have no intrinsic value. But since they were introduced to the world in 2009 by inventor Satoshi Nakamoto (a pseudonym), they have turned into a billion-dollar market and have been designated a currency by the U.S. government. Since the days when stones and shells were recognized as a means of payment, currency has taken many forms. What makes bitcoin a currency is what it does, not what it is. "To the extent it looks, walks and acts like a duck, this 'duck' is a currency,"
The US government has never designated Bitcoin a currency. The closest to an official designation of any kind is by the IRS, which has deemed Bitcoin to be "property" for taxing purposes. That's not a currency. It is true however that Bitcoin has no intrinsic value. It doesn't represent anything in particular, but people have started acknowledging it to have value. This is an entirely artificial construct, and the value is only a representation of what large groups of people agree it is worth. Because of this, there is an inherent desire to constantly value it ever higher, because that's the only way you can get a return. On the other hand, potential buyers want to value it lower so they don't spend as much to acquire it. But real currencies are being traded to acquire the property (Bitcoin), the crypto itself doesn't function as a currency very much in the real world.