Altcoins are cryptocurrencies other than Bitcoin. The term "altcoin" combines "alternative" and "coin," indicating that these digital currencies serve as alternatives to Bitcoin. There are thousands of altcoins available, each with unique features, purposes, and technologies. Some popular examples include Ethereum, Ripple, and Litecoin. Many altcoins aim to improve upon Bitcoin's limitations or offer new functionalities, such as smart contracts or faster transaction speeds. Investors often explore altcoins for diversification or potential higher returns, but they can also carry higher risks due to market volatility and varying levels of adoption.