Een altcoin is een alternatieve coin voor de Bitcoin. Op Top Altcoin Sites wordt ie als volgt omschreven:
You are constantly hearing the word ‘altcoin‘ and you are wondering what an altcoin is. Well, it is actually pretty simple. An altcoin is an alternative coin for a bitcoin. So basically, it is any coin that is not a bitcoin.
The difference with a Bitcoin is that an altcoin can’t be bought with fiat money, but you have to buy Bitcoins first, before you can trade them to altcoins. So after buying a Bitcoin, you will be able to buy a Dogecoin or a Litecoin, for example. On the other hand, mining altcoins is easier than mining Bitcoins, so we are seeing a growing amount of people who are mining alternative coins instead of BTC.
http://topaltcoinsites.com/what-is-an-altcoin-and-what-is-the-difference-with-a-bitcoin/