Alt Coins implies a category of cryptocurrency that is alternative to the digital currency Bitcoin. After the success story of Bitcoin, many other peer-to-peer digital currencies have emerged in an attempt to imitate that success.
Many of the altcoins are built up on the basic framework provided by Bitcoins. Thus most altcoins are peer-to-peer, involve a mining process and offer efficient and cheap ways to carry out transactions on the web.
Examples of altcoin include Litecoin, Dogecoin, Ripple, Cardano, Tron, and many more.