All the coins available in the market other than Bitcoin are altcoins. Altcoins are too many types, like:
Stablecoins are coins with stable values. like USD coins and DAI.
MemeCoin began as a joke but gained popularity over time. like Dogecoin
Privacy Coin, similar to Zcash, protects user privacy by concealing transaction details.
Platform coins are used to build and run decentralized apps such as Ethereum and Solana.
Layer 2 tokens, Asset-backed Tokens, Fork Coins, Governamce Tokens , Security Token, these are also altcoins available in the market.