And alternative cryptocurrency to bitcoin. Bitcoin being the first cryptocurrency, any variation thereon is an Altcoin (or alt-coin)
"Litecoin is my favourite altcoin because it makes ASIC mining more difficulty"

"Namecoin is sort of an altcoin, but also a domain name system"
by Vinceypoos December 3, 2013
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An new alternative to the altcoins already available in the crypto currency scene.
Platinumcoin and limxcoin are altcoinatives to litecoin and darkcoin.
by Cointopay January 6, 2015
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