What are Cryptocurrencies

A cryptocurrency (or crypto currency) is a digital asset designed to work as a medium of exchange that uses strong cryptography to secure financial transactions, control the creation of additional units, and verify the transfer of assets. Cryptocurrencies are a kind of alternative currency and digital currency (of which virtual currency is a subset). Cryptocurrencies use decentralized control as opposed to centralized digital currency and central banking systems. The decentralized control of each cryptocurrency works through distributed ledger technology, typically a blockchain, that serves as a public financial transaction database.

Bitcoin, first released as open-source software in 2009, is generally considered the first decentralized cryptocurrency. Since the release of Bitcoin, over 4,000 altcoins (alternative variants of Bitcoin, or other cryptocurrencies) have been created.

According to Jan Lansky, a cryptocurrency is a system that meets six conditions:
The system does not require a central authority, its state is maintained through distributed consensus. The system keeps an overview of cryptocurrency units and their ownership.
The system defines whether new cryptocurrency units can be created. If new cryptocurrency units can be created, the system defines the circumstances of their origin and how to determine the ownership of these new units. Ownership of cryptocurrency units can be proved exclusively cryptographically.
The system allows transactions to be performed in which ownership of the cryptographic units is changed. A transaction statement can only be issued by an entity proving the current ownership of these units.
If two different instructions for changing the ownership of the same cryptographic units are simultaneously entered, the system performs at most one of them. In March 2018, the word cryptocurrency was added to the Merriam-Webster Dictionary.