Cryptocurrency is a digital or virtual currency secured by cryptography, which makes it nearly impossible to counterfeit or double-spend. It is a form of digital asset based on a network that is distributed across a large number of computers, allowing it to exist outside the control of governments and central authorities. Cryptocurrencies do not exist in physical form like paper money and are typically not issued by a central authority. Instead, they use decentralized control as opposed to a central bank digital currency (CBDC). When a cryptocurrency is minted, created prior to issuance, or issued by a single issuer, it is generally considered centralized.

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.

Cryptocurrencies are usually built using blockchain technology, which describes the way transactions are recorded into "blocks" and time-stamped. The use of blockchains addressed a problem faced by previous efforts to create purely digital currencies: preventing people from making copies of their holdings and attempting to spend it twice. The first cryptocurrency introduced was Bitcoin, which was founded in 2009 and remains the best-known today. Other popular cryptocurrencies include Ethereum, Cardano, Solana, Dogecoin, and XRP.

In summary, cryptocurrency is a digital or virtual currency secured by cryptography that uses decentralized control as opposed to a central bank digital currency (CBDC). It is built using blockchain technology and is not issued by a central authority. Cryptocurrencies are used as an alternative payment method or as an investment, and their prices are extremely volatile.