What is the mean of crypto?

A crypto currency is a digital currency which employs encryption techniques to regulate the generation of units of currency and verify the transfer of funds, operating independently of a central bank.

There are many types of crypto currencies, some similar to Bitcoin (BTC), some with these features but more centralized like Ripple (XRP) and others that don't really have anything specific in them like Ethereum (ETH). The two main differentiators between types of coins are whether they use "proof-of-work" or "proof-of-stake" algorithms. Proof-of-work is a method for generating an algorithm hash that must be done in order to add a block to the blockchain.