Virtual currency is a digital representation of value, other than a representation of the U.S. dollar or a foreign currency ("real currency"), that functions as a unit of account, a store of value, or a medium of exchange.
-IRS
While virtual currency has been around since 2009, it has become better know over the last couple of years. Although there are now dozens of them, some of the most popular names are bitcoin, ethereum, dogecoin and litecoin.
All convertible currency such as cryptocurrency is considered a capital asset for most taxpayers. You invest in virtual currency in the hopes that it will increase in value.
The price of a cryptocurrency is based on one unit, and the pricing is based on the per-unit value, which goes up and down just as a unit of stock would on a stock exchange.