A crypto currency / crypto is a digital asset with uses cryptography as a means to secure the transactions, verify transfers and in some cases control creation of new coins.
They are decentralized, which is what differs them from the likes of Paypal.
Payal and the like although are digital are tied to fiat currencies and central banking systems.
So with Crypto currency there is no need for the traditional banking system.
Crypto Currency Blockchain
Each crypto currency / crypto distributes a ledger which is usually a Blockchain that allows public viewing of the financial transactions.
Crypto currency / crypto in most cases runs anonymously so it can be hard to trace transactions to a single user.
Bitcoin is considered the first (released as open-source software in 2009), since the release, over 4,000 alt coins (alternative variants of bitcoin, or other cryptocurrencies) have been created.
Transactions cannot be reversed, once a payment is made through the Crypto currency / crypto network the funds can not be recovered or reversed, this can be problematic for people buying goods or services from unknown or untrusted sources.
Due to the anonymity and irreversible payments the criminal have adopted using Crypto currency / crypto, but as Crypto currency / crypto are now more mainstream it is not just used by criminals and many big companies and genuine businesses are accepting this new form of payment.
Today Crypto currency / crypto have become a global phenomenon known to most people.
While still somehow geeky and not understood by most people, banks, governments and many companies are aware of its importance.
Some people in the financial industry think it's just some giant ponzi scheme, well I say look at your own countries money, isn't that just a giant ponzi scheme.
Think about the UK, people go to work get taxed and then that money is spent, it can only keep getting spent if people pay in.
Those working are funding the lives of those who don't.
Others think it's magic internet money, well it's not far off that.
The reality is that it serves as a unit to enable trade.