First there was bitcoin, and it was good. Then came a whole host of other coins. They were known as "altcoins" as in "alternative to bitcoin". The name stuck, and now anything that isn't bitcoin automatically gets called an altcoin. Some will debate whether that's changing--that certain blockchains are foundational, like Ethereum, Ripple, and Bitcoin Cash--but for bitcoin maximalists, everything that isn't bitcoin, regardless of whether it's a utility token, a blockchain, a security, or whatever, will be an "altcoin."