Altcoins, short for alternative coins, denote any cryptocurrency other than Bitcoin and sometimes Ethereum. Altcoins serve similar purposes as BTC and ETH but may use different consensus mechanisms and technologies. Bitcoin and Ethereum may dominate the cryptocurrency market, but the remainder of the market share comprises altcoins.
Altcoins represent digital currencies designed and developed on the blockchain without the intervention of a centralized authority such as a government or a bank. They leverage public blockchain networks for functioning and gain value based on the usage level of their underlying blockchain infrastructure and their demand as investment instruments in exchanges.