An altcoin is short for alternative coin, a term used to describe all cryptocurrencies other than bitcoin. Just like bitcoin, every altcoin is decentralized and uses blockchain technology. The term is also used to refer to tokens rather than coins, including the most popular standard for token issuance, the ERC-20 tokens, that exist on top of the Ethereum blockchain.
While sharing some similarities, each altcoin has its own functionality. Some of the popular types of altcoins include mining-based crypto assets; stablecoins or tokens that have the same value as fiat currency; governance tokens or tokens that represent voting rights in blockchain projects, and so on.
According to Coinmarketcap, as of August 2021, there were more than 8,000 altcoins circulating in the market, with Ethereum (ETH) and Cardano (ADA) as the largest altcoins by market capitalization.