Altcoins or alternative cryptocurrency coins are coins that are an alternative to Bitcoin.
Generally speaking, all altcoins are variants or forks of Bitcoin. Meaning, it was built using ‘Bitcoin’s open-sourced’, the original protocol with changes to its codes. Therefore giving birth to an entirely new coin with a new set of features.
Some examples of altcoins that are variants of BTC’s codes are Namecoin, Peercoin, Litecoin, Dogecoin, and Auroracoin.