What is cryptocurrency?
A digital currency in which code based on cryptography controls the generation of units of currency and verification of transactions for transfer of funds. A cryptocurrency is not backed by a government or a central bank of any country/countries. The account keeping is done in a distributed manner. Think of it as a distributed ledger one in which you can’t alter the order of transactions.
In short, you can call it people’s money. Money created by the masses, for the masses and controlled by the masses.
Such money has various advantages compared to FIAT currency. That is the whole reason many banks and governments are opposing the adoption of cryptocurrencies. Cryptocurrencies take the power out of centralised power centres, whether they are governments or central banks.