Altcoin means alternative coin, also a cryptocurrency or digital currency and is different to Bitcoin. Bitcoin and altcoin are competing for a period of time if I'm not wrong. There are different altcoins such as Monero, Litecoin, Dash,  Etherium, Dogecoin and more. These altcoins are produced by different projects in ICO. Inwill suggest you to read on articles regarding with altcoins for you to understand it more.