What is an altcoin?

An altcoin is any cryptocurrency other than Bitcoin, short for "alternative coin." The term matters because it groups thousands of very different projects, from Ethereum's smart contract platform to small meme tokens, under one label, so it's worth checking what a coin actually does before assuming "altcoin" tells you anything about quality or risk. Ether, Solana, and Dogecoin are all altcoins despite having almost nothing in common beyond not being Bitcoin. Some altcoins power blockchains with real transaction volume; others exist mainly for speculation. Traders often watch "alt season," a stretch when altcoins rise faster than Bitcoin, as a sign that risk appetite in the market is increasing. Because the category is so broad, comparing an altcoin's market cap, use case, and team is more useful than treating the label itself as a signal.