ISK

From EVEWiki

ISK, or Inter-Steller Kredits are the in game currency of the Eve-Online universe. Items such as single rounds of ammunition can be purchased for a few ISK, but sales of rare or powerful equipment can fetch hundreds, millions or even billions of ISK.

One of the largest single transactions for liquid ISK was the sale of a Hulk Tech 2 ship Blue Print Original which fetched over ISK70b following the RMR content update.

ISK is also the international standard currency code for Icelandic Krona. Iceland is the home country of CCP, creators of Eve-Online.

There are also numerous strategy guides that focus on advice on making ISK, one example being Killer Guides' Eve Online ISK Guide.

It is against the Terms of Service to sell ISK for out of game money; however, ISK can be bought with out of game money through the 30 day pilot licenses (PLEX) sold by CCP which can then, with restrictions, be sold in game for ISK. There is also an approved way to trade time codes for ISK via the forums.

The point of the PLEX is that players who generate enough ISK monthly can afford to pay for their in game time entirely with ISK by buying PLEX and then redeeming them to pay for game time with ISK. For example on 2009-09-12 PLEX were fetching around 300,000,000 ISK on the market, thus playtime was about 10M for 1 day, which isn't that difficult to make for an established player.