A cryptocurrency is a purely digital and decentralised form of payment.
This means that no bills or coins are being used and that money transactions are being executed online. Also, there is no central financial institution regulating the crypto currencies.
Anybody who has followed the bitcoin hype knows that crypto currencies are being traded actively. Whoever invests in these currencies can therefore earn or lose a lot of money depending on how the market develops. These currencies are being traded on online exchanges and the value developments depend on the demand. In general, a cryptoinvester is seeking the next big thing, the next currency that will explode in value.