Cryptocurrencies are a form of currency that is purely digital. In essence, it is a series of entries in a public database. To create a new entry or change one, specific conditions must be met. This is the basis of all currency.
What makes cryptocurrency unique are two principles. The first is that the currency is secured by cryptography hence cryptocurrency. This means that algorithms are responsible for the security of the coins rather than an entity or person.
The second principle is that cryptocurrency is 100% decentralized. This means that it is not ruled or governed by any singular entity and was instead built on a sophisticated communal concept with extensive digital safeguards. This communal system became the blockchain which is the backbone of this whole economy.
The idea behind these principles was that people would be able to use their currency without any outside intervention. No one can block you from using cryptocurrency or making a transaction and as a communal economy the currencies cannot be subjected to things like inflation, enforced balances, or political intervention. Your coins are stored in a digital wallet. They were also created to have a predetermined finite amount of currency that will ever be distributed, however nowadays there are some currencies that do not have a cap.