A Cryptocurrency (or crypto) is a digital asset secured by cryptography. Cryptocurrencies are based on the so-called distributed ledger technology, whereby all transactions are stored on the blockchain.
Like traditional FIAT currencies, cryptocurrencies also act as a medium of exchange, however with no intermediaries (e.g. banks) monitoring the transactions.
In addition to Bitcoin, which is considered the first cryptocurrency, there are over 10,000 different cryptocurrencies today. These cryptocurrencies are called altcoins (alternative coins).