FFXI Final Fantasy XI Exploits
Exploits as described in MMORPG's are techniques or strategies to make use of a feature to gain an unfair advantage over others. You could call them cheats, but technically they are bugs. They allow players to do things normal players would not be able to do. Sometimes they affect the balance of the game, sometimes they do not.
Exploits are usually kept in secret or to a select few who know about them. The honest ones would report them to the developer so that they could be fixed. There is one place where they keep an updated list of exploits, that place is at Skryer. The developers work hard to fix exploits as soon as they're found so that players can not take advantage of them. It is for this reason why exploits only work for a limited time and then they are fixed. In some extereme cases players are banned or given penalties for using exploits, especially those which affect the entire player-base.