Virtual Currency is any currency that is not printed on paper or stamped into metal. It's virtual because it only exists in the virtual world. Virtual currency potentially can represent physical currency.

Digital currency is virtual currency that specifically exists in the digital space, meaning that it maps to some digital storage, likely a hard drive somewhere.

Cryptocurrency is both digital and virtual currency that is created based on some cryptographic algorithm (Sha-256, Scrypt, etc). No one "mints" this currency, they solve cryptographic algorithms using hardware and electricity to get the representation of one unit of value, typically called a "coin". Bitcoin, Litecoin, and altcoins are all cryptocurrencies.