NCoin is the premium currency that can be used in the cash shop to buy items to improve the quality of life in the game. It is purchased with real world money. Many of the items in the cash will also be purchasable with in-game currency as well. However, premium membership is only purchasable with NCoin.
80 NCoin is equal to $1 USD, and can be used with other NCSoft games as well, such as Wildstar. NCoins can be purchased with PayPal or a credit card.